Iphone 4 not sending or receiving messages?

I god an iPhone 4 today, complete with unlimited talk and text but a limited data plan. When I first got my phone and charged it, I was able to text my friend for about an hour, and since then it will NOT receive or send ANY texts at all.iMessage isn't working for some reason, it'll just sit there and say "waiting for activation" and won't change at all. I've logged in to my itunes account through it and everything, and nothing. I also backed it up and restored it like most sites said and it STILL will not work. Any tips on how to fix this issue? It's very frustrating, and answers soon would be great. Thanks.
Also, not sure if worth mentioning, when I send a text it doesn't have the exclamation mark near it saying it failed to send, but it doesn't say it sent either.

Added (1). Also I'm on AT&T. I'm not sure if that'd be an important detail either.

Try this, From the home screen, tap Settings.

Tap General.

Tap Reset.

Tap Reset Network Settings.

Tap Reset Network Settings.

All network settings will be restored to factory defaults.

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