Can the iphone 4 or 4s be on a 50$ tmobile 4g monthly plan?

Can the iphone 4 or 4s be on a 50$ tmobile 4g monthly plan?

Yes, but it HAS TO BE A GSM unlocked phone. Not CDMA. CDMA is used for Verizon GSM is used for At&t and T-mobile etc.

Btw the iPhone 4-4S are both 3G phones.