Your Suncom SIM card will only work in a Suncom phone. SIM cards are not interchangeable between different carriers but only within your particular carrier. So it will not work on a TMobile phone, unless you have a phone that is unlocked.
Technically it should. However, T-Mobile is shutting down Suncom's switch access and converting them to their own. This means that you will need a T-Mobile sim asap.
No each SIM card is unique to the carrier. So cards from other carriers will often not work. However if you have an active SIM and you have an active acct then it may work if the phone is digital which i believe that T-Mobile is, as well as some of the other major carriers.
from my knowledge you will have to unlock the phone to allow transmissions from a different carrier. changing the vpn and apn adress will help also in the configuration , lastly you will have to contact suncom to have them change the settings so you can get internet and text