The glass and LCD are fused together. I don't think that it's glue, but I could be wrong. If you read Replacement iPhone 4 Display Assembly Parts it should clarify some things.
There currently is not a jailbreak for iOS 6. So, if you update now then you can't jailbreak it. If you keep 5.1.1 you can jailbreak it here. If you jailbreak it you will not be able to update to 6.0. None of these thing will fix your no service problem.
Maybe you didn't connect the earpiece connector correctly while putting the phone back together. Try reopening the phone, making sure all the connections are secure.
You might want to try this: 1. Save everything on your phone not through a backup (Write a list of apps, sync notes, contacts, etc. through iCould and save photos/videos on your computer) 2. Restore with the latest software 3. Put everything on the iPhone, not from a backup (download apps, setup iCloud, and put the photos/videos on the phone.
I've looked through my 4S a lot, there's no barcode inside it, but you can find it in the settings of the phone, a barcode on the original box and by connecting it to iTunes.
The ribbon cables for the LCD and touch screen can be bent or torn easily, so the cables could be damaged and you couldn't tell. I would try another LCD and be very careful not to bend or tear the cables.
70% will work, but the higher the concentration the better.