Can you use an AT&T iphone 5 with staighttalk?

I have been using an android phone that I bought from the straighttalk company for a while, but recently was given an AT&T iphone 5. I read that there's a card you can buy for the bring your own phone program, however, I do not want to have to change my number. Also, if you have done this, please let me know if you have had any issues!

Only if the original owner had ATT unlock the phone from ATT and it's GSM signal. Straightalk uses CDMA signals anyway. So if the phone is unlocked, yes. If not, no. How do you know/tell? Settings > General > About > see next to network. If it says ATT then you can't. Best luck.

Thank you!

Yes, you can. Straight Talk uses both cdma and gsm towers. Ask Straight Talk for an AT&T sim card. Pop it in and you may have to change the APN but you can google how to do that. You do not need an unlocked phone and this other person is misinformed that they use only cdma. They use All the major carriers.