IPhone won't connect to cellular data network?

My iPhone will not connect to cellular data network at all. It was just working a few hours ago but suddenly it won't. I've tried restarting it twice. I've tried turning on and off airplane mode waiting 5 seconds in between. And turned off and on cellular data. I've reset the network settings too but nothing is working. What can I do? I'd rather not have to restore iPhone as new. I have an iPhone 4S and I don't have iOS7 because I never had enough space to download it. Any suggestions?

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