Can i still get service on my iphone 5?

I know i screwed up but bear with me i bought a iphone 5 from craigslist and the carrier is tmobile. At&t and tmobile arr compatible so i tried to use it for at&t. Well it turns out the phone is locked. So does that mean i can only use it for tmobile or i can't use it at all? If i can't use it at all what do you think i should do?

If it was listed for T-Mobile then it would only work for T-Mobile. So of course when you tried to use it for AT&T it wouldn't work. AT&T & T-Mobile are GSM carriers but that doesn't mean phones for one work with the other out of the box.

Yes, it means the phone can only work for T-Mobile. You could get it unlocked if you want it on AT&T.