What would cause an iPhone to cut on and off constantly?

I have had my iPhone for about a year and a half now. It has been dropped a few times but only having caused a few scratches and has never had water damage. Yesterday, in the top bar it showed "Searching… " instead of my provider, Verizon. A little after that the "Restore Needed iPhone can't make or receive calls. Restore from iTunes." notifications popped up. Then a little after that it started cutting itself on and off and continues to do this every 3 or so minutes. I tried to restore the phone by connecting it to iTunes but it doesn't stay on long enough to restore. The only thing I know I haven't done is updated to iOS 5.1.1. Would this cause all these things to happen?

How to get unlocked iPhone to Virgin Mobile?

I like the Virgin Mobile Data plans and I recently bought an iPhone 4S Unlocked in factory condition. I saw a Virgin Mobile iPhone 4S sim card on eBay and I was wondering if it were possible to switch the Sim cards. Would my phone be on the Virgin Mobile carrier group? If so, what procedures should I go through. If not. What can I do? I don't want to buy one of VM's 700 phones?

What type of glass should I by for my iphone?

I'm trying to replace my iphone 4 (not a 4s) glass since it was dropped and the glass shattered.Am I able to buy just any type of glass, or is there a specific kind of glass? Is it possible to buy the front part of the iphone? So that I have an entirely new front part that looks brand new and I can replace the broken one with that? Or what kind of advice would you have for me in terms of buying new glass?