Switching carriers
How to Activate a Phone on Any US Carrier
What to check before you start, how to keep your number, and what to do when the phone activates but calls still will not connect.
Activating a phone takes two things: a phone the carrier will accept, and a SIM or eSIM from that carrier. The rest is paperwork. What actually goes wrong is almost never the activation itself. It is finding out afterwards that the handset is still locked to the carrier you left, or that it was never certified for calling on the new network.
So check compatibility first, then decide whether you are keeping your phone number. Keeping it changes the order of the steps, and doing those steps in the wrong order is how people lose a number permanently.
Three checks before you activate anything
1. Is the phone unlocked?
A phone bought on an installment plan is normally locked to that carrier until it is paid off and has been in service for a set number of days. The carrier you are leaving has to unlock it. The carrier you are joining cannot.
Ask the old carrier to unlock the device before you start anything else. If you wait until after you cancel, you are asking a company you no longer pay to do you a favor.
2. Will the new network actually carry your calls?
Every US carrier shut down its 3G network in 2022. Calls now run over VoLTE, and carriers only allow VoLTE on handsets they have certified. A phone can show full bars, pass a data test, and still fail to complete a single call because the carrier never added that model to its list.
Run your IMEI through the new carrier’s compatibility checker before you buy a SIM. Dial *#06# to get the IMEI. This one check prevents most activation failures.
3. Does the phone take a SIM at all?
iPhone 14 and later sold in the United States have no SIM tray. They are eSIM only. Most recent Android flagships support eSIM and still have a tray. If the phone is eSIM only, you cannot move service by swapping a card, and the carrier has to support eSIM activation.
Activating with a new phone number
This is the simple path. Nothing is at risk because there is no number to lose.
- Confirm the phone is unlocked and on the carrier’s compatible device list.
- Buy the SIM or start the eSIM activation from the carrier.
- Insert the SIM, or scan the eSIM QR code, and follow the prompts.
- Restart the phone once service appears. This forces it to pick up the carrier settings.
- Place a test call and load a web page over cellular data with Wi-Fi turned off.
Activating while keeping your number
Do not cancel your old service first. A phone number can only be ported off a line that is still active. Cancel first and the number is released, and once it is released it is usually gone for good. Start the port with the new carrier and let the port itself close the old account.
To move a number you need two pieces of information from the carrier you are leaving, and neither one appears on your bill:
- Your account number. This is the carrier’s internal number, not your phone number.
- Your transfer PIN. Sometimes called a port-out PIN or number transfer PIN. It is not your voicemail password and usually not your account PIN.
- Give both to the new carrier along with the billing name and address exactly as the old carrier has them. A mismatch here is the single most common reason a port fails.
- Keep the old phone powered on until the new line is working.
Most wireless-to-wireless transfers finish within a few hours. If yours is still pending after a business day, something you supplied did not match the old carrier’s records. Every US carrier hands over account numbers and transfer PINs differently, and some make it deliberately awkward. Look up your current carrier for the exact steps.
eSIM or physical SIM
An eSIM activates in minutes with no shipping, and it lets you keep the old line running on the same phone while the new one is set up. That is genuinely useful during a switch. The trade-off is that moving an eSIM to a different phone later usually means contacting the carrier, where a physical SIM moves by hand in ten seconds.
If you switch phones often, take the physical SIM when the phone offers a tray. If you are switching carriers today and want service working today, take the eSIM.
Activation finished but the phone has no service
Work through these in order. They are listed by how often they turn out to be the cause.
- Restart the phone. Carrier settings often do not apply until it does.
- Check the APN. If calls and texts work but mobile data does not, the APN is wrong. The carrier publishes the correct values.
- Check VoLTE. If data works but calls fail, the carrier has not provisioned VoLTE for that IMEI. Only the carrier can fix this, and on an uncertified handset they may not be able to.
- Confirm the phone is unlocked. A locked phone will often register on the network and then refuse to pass traffic.
- Check that the port completed. While a transfer is pending, the new line can show service and still not receive calls.
Already know where you are going?
Each of these walks you through switching to that carrier: what to check first, how to keep your number, how to activate, and what leaving your current carrier actually costs.
On Verizon’s network
On T-Mobile’s network
On AT&T’s network
Some links above are affiliate links. We may earn a commission if you switch through them, at no cost to you. We recommend by network compatibility first, not by what pays most.
Find your carrier’s activation and transfer details
Account numbers, transfer PINs and port-out steps, by carrier. Free, no signup.
Common questions
How long does activation take?
A new number is usually live in a few minutes. Keeping your existing number takes longer because the two carriers have to agree the number is yours, and that is normally a few hours.
Can I activate a phone I bought used?
Yes, if it is unlocked, not reported lost or stolen, and on the carrier’s compatible device list. Check the IMEI with *#06# and run it through the carrier’s checker before money changes hands. A blacklisted IMEI cannot be activated on any US carrier.
Do I need to cancel my old plan?
Not if you are keeping your number. The transfer closes the old line for you. Cancelling first releases the number and you will probably lose it.
Why do I need a transfer PIN when I already have an account PIN?
They are different values at most carriers. The transfer PIN exists specifically to stop someone moving your number without your knowledge, which is why carriers generate it separately and why it often expires after a few days.
My new SIM works for data but not calls. What is wrong?
Almost always VoLTE. The carrier has not enabled voice over LTE for your device. Contact the new carrier with your IMEI and ask them to check whether the handset is provisioned for VoLTE on their network.
Best Cellular is a free reference site published by Assertive Holdings, LLC. Some links on this site are affiliate links, which means we may earn a commission if you switch carriers through them, at no cost to you. It does not change what we publish: carrier information on this site is verified against the carriers’ own documentation. Verified September 2026.