Can you use a T-mobile SIM card in a T-mobile prepaid phone?
Yes,provided the T-Mobile prepaid sim card phone is not locked with any other different netork.If it is, then you need to unlock.To unlock you can approach any legit unlocking vendor like Unlocking4u.com and avail their permanent unlocking solution by specifying the mobile make,model,country,locked network.Based on the availability you can get the unlocking service along with free unlock instructions.