My phone won't receive or send messages from or to certain people. To some people it works and others it doesn't. What can I do to fix this?
The first thing that comes to mind is to check that reply path is not selected in the messaging settings. This setting means that if you reply to a sms, it uses the sender's messaging center, and usually using another operator's messaging center is not allowed. However, this shouldn't affect your ability to receive messages.