Can't send and receive SMS/MMS/iMessages after restoring iPhone from a backup
I can't receive and send any type of messages with my iPhone 3GS (iOS 6.1.6) after restoring it from my old backup (also 6.1.6).
Messages that I'm sending are disappearing immediately after the moment they are sent and they are never delivered. The first time I restored my iPhone I could send and receive messages for 1 day, and I couldn't do it on the next day. This time I was able to send and receive messages for 10 minutes.
I have used the methods Apple recommends for problems like this, but it doesn't help.
MacBook Air (13-inch Mid 2012), OS X Mountain Lion (10.8.5)