How to reactivate my iPhone 4S off Sprint after I restored it?

I had the iOS 7 beta version and I didn't really want it anymore so I restored my phone back to the iOS 6.1.3 and my sister removed all my music onto another file so I didn't have my music on iTunes. So she added her music onto my iTunes and then when I tried updating my apps it was signed on to her apple ID but when I went to settings it says it was signed in on mine. So I restored everything and I put everything back to normal but now the phone just doesn't want to activate. Do I have to take it to a Sprint store later or will it activate itself? It shows the service bar that's it, no 3G or Sprint. It actually says it's not connected to any network. So what should I do and how do I do it?

You should register your UDID with a site like http://www.instantudid.com/ and then activate iOS 7.