Read the modem's Manual - it will tell you all the AT commands and S-Registers available to configure the modem.

You will probably want to fix the baud rate, etc;
You will need to set the appropriate flow-control option.

Try connecting the modem to a terminal, and answering the call manually - make notes of what you have to do.

You should also look at setting your modem to "terse" or "numeric" response mode - as I've said many times before, this is by far the easiest way to conctrol a modem from software:
http://www.8052.com/forum/read.phtml?id=67282

trying to parse the "verbose" or "text" responses is a lot of work for no benefit!