Hi, I've had my Sony Ericsson m600i for a couple of months now. My problem is that sometimes i can receive calls and other times i don't recieve anything. My friends have told me that when they call me sometimes, it says that im unavaiable. Its not the sim cause i tested it on another phone for a couple of days so its not the sim. Any ideas on what the problem is. Also, I can call out and send and recieve sms.