I need the the cell-id information to display in my iphone app, the app sends AT commands to the modem but...I do not know how to read the modem messages. Please help me.
if you are asking in context of the iPhone, then I don't think you are allowed to do that with the official SDK.
You should look at the source code of the unlock tools by the team because they send AT commands to read data from the iphone modem.