Pre-Switch Checklist: What to Check Before Changing Carriers

Switching carriers takes less than an hour on the day itself, but the preparation matters. Arriving at the new carrier’s sign-up flow without a transfer code, with a locked phone, or without migrating your two-factor authentication (2FA) accounts can cause delays, failed ports, or temporary loss of access to critical services.

This checklist covers the eight categories to verify before you switch. Work through them in the order shown — each step builds on the one before. Allow two to four weeks for the full preparation so no single step becomes a last-minute blocker.

1. Confirm Your Phone Number Portability Status

Number portability — the right to keep your number when switching carriers — is a legal mandate in most countries with significant mobile markets. The process requires a transfer credential from your current carrier. Without it, your new carrier cannot initiate the port.

The name of this credential varies by country:

Confirm that your account is eligible for porting. Most carriers require your account to be active and in good standing. Some carriers apply a temporary porting hold after recent account changes such as a SIM swap or address update; the duration varies by carrier, so check before requesting a transfer credential.

For a full explanation of how number portability works and what to do if a port fails, see Mobile Number Portability (MNP) Explained.

2. Check Your Phone’s SIM Lock Status

A carrier-locked phone only connects to the carrier that applied the lock. Even if your number ports successfully, a locked device will show no service on the new carrier’s SIM until the lock is removed.

iPhone: Open Settings → General → About → Carrier Lock. If it reads “No SIM restrictions,” your phone is unlocked. Any other message means it is locked.

Android: Insert a SIM card from a different carrier. If mobile data and calls work, the phone is unlocked. If you see “SIM not supported” or “Invalid SIM,” the phone is locked.

If your phone is locked, request an unlock from your current carrier before initiating the switch. Processing times vary:

• In the UK, Ofcom banned the sale of locked handsets from 17 December 2021. Phones bought after that date are already unlocked.
• In the US, each carrier sets its own policy. Verizon unlocks automatically once the device payment plan is paid off. AT&T requires at least 60 days from purchase plus a paid-off balance. T-Mobile unlocks devices purchased on or after January 27, 2026 once fully paid.
• In most other markets, request an unlock through the carrier’s website or app. Online requests are typically free; in-store requests may carry a fee at some carriers.

Allow several business days for the unlock to process. Confirm the unlock is active before the day you switch.

For a full breakdown of how to check lock status and how unlock policies work by region, see SIM Lock and SIM-Free Explained.

3. Audit Your Two-Factor Authentication (2FA) Methods

This is the most time-sensitive preparation step. Many services use your phone number for SMS-based two-factor authentication. During a carrier switch, there is a window — ranging from a few minutes to a couple of hours — when SMS delivery is unreliable on both the old and new SIM. Triggering an SMS 2FA request during this window can lock you out of a service temporarily.

Before switching, do the following:

1. List every account that sends a verification code or login alert to your phone number. Start with banking, email, brokerage, and any work account.
2. Log in to each account before the switch begins, while SMS delivery is reliable.
3. Where possible, migrate from SMS 2FA to an authenticator app (such as Google Authenticator, Apple Passwords, or Authy). Authenticator apps generate codes locally and are unaffected by carrier transitions.
4. If SMS 2FA is the only option for a service, note it, and avoid logging out of that service on any device until after the port completes.

Backup codes for authenticator apps and recovery codes for accounts are distinct from SMS codes. Download and store them securely before the switch.

If you use SMS 2FA specifically for secure access to your email or cloud backup, resolve this before your phone number moves to a new carrier.

A further risk worth noting: some financial institutions and workplace systems automatically flag a number change as suspicious activity and may freeze login access pending a manual review. If you manage accounts with this behaviour, notify the relevant institution in advance or confirm their process for number changes.

4. Check Your Contract End Date and Early-Termination Fees

Switching before a minimum contract term ends typically triggers an early-termination fee (ETF). The fee amount and calculation method vary by carrier and country.

What to check:

• The contract end date. This is shown in your carrier’s account portal, on your paper contract, or on your monthly bill.
• Whether an ETF applies and, if so, how it is calculated. Some carriers calculate it as a flat fee; others base it on the number of months remaining.
• Whether the ETF reduces over time (many contracts pro-rate it across the term).

In most countries, carriers are not permitted to use an outstanding ETF to block a number port — they can only demand payment. However, the obligation to pay the fee remains after the port completes.

If you are within a few weeks of your contract end date, it is generally worth waiting to avoid the fee. If you are early in a contract, compare the ETF against the savings from switching — use the provider comparison to size up what competing carriers currently offer before you run the numbers. Factor in the first month of the new carrier’s service when making this comparison — some carriers bill a partial first month plus the following full month on the first invoice.

Also check whether your current carrier is in a promotional period that provides a discount or bonus data allocation. These perks are account-level and expire when the account closes; they do not transfer with the number.

Prepaid accounts typically do not have ETFs. Month-to-month postpaid contracts also typically do not carry ETFs.

5. Check Your Device Installment Balance

If you purchased your phone through the carrier on a device financing or installment plan, the balance is separate from your service contract. In most countries, you can port your number even with an outstanding balance — carriers cannot block the port — but you remain liable for the remaining payments.

What to check:

• The remaining installment balance. This is on your monthly bill or in the account portal.
• Whether your carrier requires the balance to be paid in full before they will unlock the device. Unlock eligibility and porting eligibility are separate. Even if the port proceeds, a locked phone will not work on the new network.
• Whether paying off the balance early incurs any interest or fee.

If the installment plan balance is large and you want to avoid parallel payments, pay it off before switching — or factor those payments into the total cost comparison between your current and new carrier.

6. Collect the Account Details Your New Carrier Will Ask For

Porting requires your new carrier to submit a request on your behalf. A mismatch between the details you provide and what the current carrier holds on file is the most common reason ports fail.

Gather the following before starting sign-up:

• Phone number you want to port.
• Account number with the current carrier — this is an internal identifier, not your phone number. It is on your bill or in your carrier’s online portal.
• Transfer credential (PAC, Number Transfer PIN, RIO, or equivalent — see section 1 above).
• Registered name on the account, exactly as it appears. A middle name or suffix difference can cause a rejection.
• Billing address on the account.
• Account PIN if your carrier uses one (distinct from the transfer PIN in some systems).

If you are on a family or shared plan, confirm whether your line is owned by a primary account holder and whether that person needs to authorise the port.

If any detail is uncertain, log in to your current carrier’s account portal and download or screenshot the account summary page. Having this on hand prevents delays during the new carrier’s sign-up form.

7. Back Up Your Device and Note What Will Not Transfer

The port transfers only your phone number. Content stored on your device or the carrier’s servers does not move automatically.

What to back up before switching:

• Device backup: Use iCloud (iPhone) or Google One / Google Photos (Android) to create a full backup. This preserves contacts, messages, app data, and photos if anything goes wrong during the transition.
• Voicemail messages: Voicemail stored on your carrier’s servers is not ported. It remains accessible on the old carrier’s system for a limited time after the account closes. Listen to and note any important messages. If you use visual voicemail, screenshotting or noting the content is the simplest approach.
• Call logs and SMS history: These are stored on the device, not on the carrier. A device backup preserves them.
• Carrier app data: Some carriers store loyalty points, usage credits, or promotional balances in their apps. These do not transfer. Redeem or note them before closing the account.
• eSIM profile: If you are switching away from an eSIM-only setup, confirm whether the new carrier requires you to delete the old eSIM profile before or after the port. On most devices, the old eSIM profile becomes inactive automatically after the port completes, but check the new carrier’s instructions to avoid activation errors.

A device backup also ensures you can restore your phone quickly if something goes wrong during the transition — for example, if you need to factory-reset to fix an activation issue.

8. Decide What to Do with Your Carrier Email Address

Carrier email addresses — addresses that end in the carrier’s domain — are tied to your service account. When the account closes, those addresses stop receiving mail, typically within a few weeks to a few months — check your carrier’s policy for the exact window.

Options:

1. Switch to a provider-independent address before you switch carriers. Free services such as Gmail, Outlook, and iCloud Mail belong to you regardless of which carrier you use. Update every service that uses your carrier address to the new one.

2. Use a paid mail portability service if your carrier offers one. In Japan, NTT Docomo, au, and SoftBank each offer a paid carrier email portability service (application must be made within 31 days of account closure in the case of Docomo). Similar services are not universally available; check your carrier’s website.

3. Set up a mail forwarding rule from the carrier address while you still have access, redirecting incoming mail to a permanent address.

The safest long-term approach is option 1. Carrier email addresses cannot be transferred to another carrier’s domain, and the portability services that exist require ongoing payment and vendor lock-in to the old carrier.

The Day-of-Switch Sequence

Once all eight checklist items are complete, the day of the switch follows a fixed order:

1. Do not cancel your current account first. Cancelling before porting releases your number back to the carrier’s pool.
2. Sign up with your new carrier and provide your number portability transfer credential.
3. Do not trigger any SMS 2FA logins during the porting window.
4. Wait for the port to complete. Your old SIM will lose service, and your new SIM will acquire signal and the ported number.
5. Test with a call and a message before treating the switch as done.
6. Confirm your old account is closed or follow up if your carrier does not automatically close it on port-out.

Timing tip: Initiate the switch on a weekday morning if possible. Most carriers have support staff available to resolve port issues during business hours. Starting on a Friday evening or over a public holiday risks the port stalling with no support available until the next working day.

Common Pre-Switch Mistakes

Requesting the transfer code too early. PAC codes (UK) and equivalent codes in other markets have expiry dates — typically 30 days from issue. If your carrier switch takes longer than expected, the code may expire and need to be reissued.

Skipping the lock status check. A successful port to an unlocked number on a locked phone leaves you with a working number but no usable service. Check before, not after.

Assuming the new carrier holds the account open. Some carriers automatically close the old account on port-out; others require a separate cancellation call. Check your current carrier’s policy to avoid being charged for a service month you are not using.

Overlooking paired devices. Smartwatches and tablets on a cellular plan are often on a separate line within the same account. Verify whether you want to port or cancel those lines separately.

Forgetting about roaming add-ons or promotional credits. Pre-paid international roaming packages and promotional data credits are account-level, not number-level. They do not follow the number to the new carrier.

Not confirming the new carrier’s coverage at your locations. A cheaper plan on a carrier with worse coverage in your home, workplace, or commute route provides less value than it appears. Check coverage maps for the specific addresses that matter to you — not just the city-level overview — before committing. If you are still deciding which carrier to move to, how to choose covers the five criteria worth evaluating before you sign up.

FAQ

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What if I need to switch immediately with no preparation time?

The minimum viable preparation is: (1) obtain your transfer credential, (2) confirm your phone is unlocked or request an unlock on an expedited basis, and (3) log in to any critical banking or email account before the port starts so you have an active session during the SMS 2FA gap. Everything else — voicemail backup, carrier email migration, 2FA app migration — can be done after the switch completes, though it is easier before.

My phone is still under a financing plan. Can I still switch?

Yes. In most countries, a carrier cannot block a port because of an outstanding device installment balance. However, the carrier can and will continue billing you for the remaining installments after the port. Additionally, confirm that the installment balance being outstanding does not affect the carrier’s willingness to unlock your device — some carriers tie unlock eligibility to payment completion.

What should I do if the port does not complete within the expected window?

Contact your new carrier’s support first. They can check the port request status and identify whether it was rejected by the current carrier. Common rejection reasons are a name mismatch, an incorrect or expired transfer credential, or an active account lock. If the port stalls and neither carrier resolves it within the timeframe set by your country’s regulator, file a complaint with the relevant authority (FCC in the US, Ofcom in the UK, ACMA in Australia, ARCEP in France, Bundesnetzagentur in Germany).

Can I switch and keep the same phone number on two separate SIMs (dual SIM)?

No. Number portability moves the number from one carrier to another. A phone number can only be active on one carrier at a time. If you want two active numbers, you need two separate numbers on two lines. For information on running two lines simultaneously on one phone, see the guides on dual-SIM setups for travel and eSIM Quick Transfer for iPhones.

Related Guides

• Mobile Number Portability (MNP) Explained — How number porting works technically, country-by-country timing, and common failure modes.
• SIM Lock and SIM-Free Explained — How to check your lock status in seconds and how unlock policies work by carrier and region.
• How to Choose a Travel eSIM: 5 Key Criteria — Evaluating new carrier plans before committing to a switch.
• Travel eSIM Provider Comparison — Side-by-side comparison of major eSIM providers if you are switching to a travel or global plan.
• eSIM Quick Transfer: Move an eSIM to Another iPhone — How to move an eSIM profile to a new device during or after a carrier switch.