SM5100B cellular shield

Hello,

I started working with this shield a few nights ago. I want to be able to communicate with the arduino using dtmf. I was able transmit a dtmf tone at a set duration from the shield to my cell phone. During a call, if a press a number on my keypad, the tone is audible thru the speakers attached to the shield.

The question I have is, how do you detect the dtmf tone being transmitted from the cell phone to the shield, on the arduino? Is this capability in the shield/arduino or will I need an additional circuit w/a MT8870 to detect? Perhaps you can point me in the direction?

Thanks,

-ren