i have a sprint iphone 4s that im using with AT&T at the moment (unlocked via R-sim). After restoring and jailbreaking, i put in my sim and it displays the 3G symbol. After going to settings-network it gives me the option of turning on/off 3G. Its on 5.1.1. I actually find it convenient because when i had my iphone 4 i would shut off 3g to conserve battery. Just thought it was interesting and shared this.