I have an iphone 4s verizon contract phone that i want to use on tmobile prepay. I have my sim activated and have factory reset the iphone. No matter what i do the iphone says invalid sim. How do i fix this? Is the phone not unlocked? I've read online that verizon unlocked all iphone 4s's for use on any carrier. I haven't been in the phone game since the windows mobile heyday but i'm not a noob. Thanks so much for any insight.