Y does my iPhone 4S say this on iMessage?

The top part

Your service may be suspended. Depending on what service provider you have, you may be able to call a number and find out. I believe that is the problem. This could mean your transaction didn't go through or phone could be shut off.

Because you have no service. This would be better answered by your carrier. But if I were to venture a guess I would suspect service was shut off since you didn't pay your bills.

Apple has a specific article on exactly how to fix this: http://support.apple.com/.../kb/ts4268. Follow it. You WILL need the latest version of itunes on a computer.