Recive phone call

Good morning,
Im looking at building a module for my gate, where a user can call the gate and it will open. So Im looking at a GPRS module that I can put a Pay-as-you-go SIM card in, however I cannot find any documentation on how to recive phone calls on the Ardunio, the idea being to detect a phone call, look at it the number and if its an “allowed” number then to open the gate, if it isnt dont do anything, or reject the call.

Does anyone have any documentation on how to recive calls, or text messages from the SIM card using the SIM modules?

Thank you

Could this be what you are looking for:- http://www.sparkfun.com/products/9607

I have been using AT commands to send and receive SMS, make phone calls to alert me, answer incoming calls. I'm using a Motorola RAZR with USB host shield, so there will be some minor differences between my code and yours. But the basics are the same.