Can I user a t-mobile sim if the carries is Verizon?

P.S. Depending on when it was originally sold the GSM side may not be locked. Call Apple and give them the model and serial number and tell them you just want to know if the phone is locked and if yes who it is locked with. I would do that first.

Not if it's locked to Verizon, no.

If it's carrier locked, only the carrier it's locked to can unlock it.

Yes, but you will need to contact Verizon and see if you qualify to unlock the iPhone.