Can i use a straight talk sim card in a att iPhone?

Yes, you can use a Straight Talk SIM card in an AT&T iphone, provided the phone is unlocked or compatible with Straight Talk's network. Straight Talk uses AT&T's network, so AT&T phones typically work well with their SIM cards. Just ensure that the iphone is not locked to a specific carrier and that it supports the necessary bands for Straight Talk's service.