iPhone won't accept any SIM cards

Then it's likely locked to T-Mobile. Contact them, to get it unlocked. If you were a customer of theirs, they should be able to unlock it for you.

click here-> How to unlock your iPhone for use with a different carrier - Apple Support

Only the carrier it is locked to, can unlock it. Nobody here can unlock it for you.

If you don't know who the carrier it is locked to is, check in Settings->General->About->Network

As to why it may be locked, carriers or network providers will lock devices to themselves if they are bought under a 2 year plan or otherwise subsidized by them. If you bought this iPhone used, it would need to have been unlocked by the previous owner.

If you bought this iPhone brand new from Apple, then it should not be locked. What exactly happens when you insert a SIM card? Do you get an error?

amna66 wrote:

They just say your sim is not supported

Yup, that means it's locked to a specific service provider. You won't be able to use it unless you unlock it.

Where did you buy it from? Is it an imported model from a different country than your own?

Call T-Mobile and ask them to remove the lock on the SIM card. Nothing will happen until the SIM card is unlocked by T-Mobile.

Please understand though, that T-Mobile is under no obligation to do this.

Apple can not help you. Only the carrier the phone is locked to can remove the carrier lock. If it’s locked to T-Mobile, you’ll have to ask them to unlock it.

T-Mobile has a reputation when it comes to unlocking… If you are not a current customer in good standing, and the phone is not currently active on their network, it’s unlikely they will agree to unlock it.

I’m sure you can find a phone number for t-mobile on the interwebtubes if you look hard enough…

Apple cannot unlock it for you. Only T-Mobile can unlock it if it is locked to them.

You need to contact T-Mobile to get it unlocked.

Link-> https://www.t-mobile.com/responsibility/consumer-info/policies/sim-unlock-policy

Probably because it’s carrier locked. Only the carrier it is locked to can unlock it for use on other cellular providers.

Return the phone and get your money back.

And what did T-Mobile say when you contacted them and asked to have it unlocked?