Is there a way to make a non-paid off T-Mobile iphone 8 work again after it's been deactivated by T-mobile?

I put 350 down on the iPhone paid the bill a couple times and then switched the Sim to be on a different plan and never paid the bill again then T-mobile made my phone only work on Wi-Fi is there a way that I can unlock the phone

The way is to pay your bill.

Pay off the balance due.

Pay up.

You need to learn that these companies have all the control
and you can't make them do things your way.

Once you can handle that, your life will be at least a little easier.

The ONLY way is to pay off the phone (if it has NOT already gone to collections). And use this as a lesson as one of the things that can happen if you do not pay your bills.

And NO, once a carrier blacklists the phone's IMEI (GSM carriers) or ESN (CDMA carriers), it stays blacklisted until the ORIGINAL owner of the bill, pays it, in full. Sure you can PAY to have the phone unlocked, but until it is paid off, you own a rock, that looks like an iPhone.

No, it is now blocked from the mobile network.

Also get ready for the debt collectors or legal action, as you still owe the balance of the money for the contract, plus interest and likely other recovery or court fees.

The _only_ practical solution is pay off the contract in full immediately, then grovel and beg to T-Mobile support to see if they will unblock the phone.

They have no obligation to unblock it as you breached the contract and committed an act of criminal fraud against them.