This is the shield.
And this shows where the connections need to be made.
The Pi cannot record Audio without an extra USB card. The problem is, the Pi wont be able to do any kind of audio for you here. It might just be a really overpowered board to run this GSM.
One option is tho install RasPBX (Asterisk server) for VoiP. That will make sense. You can then connect all phones in your house (Using a SIP Client) to the Pi. You can call each other when in the same network, or if the GSM shield gets a call then all SIP clients will ring, audio recording. But you need to be able to record audio on the Pi. USB Sound card.
The other options are to use the Shield as a way to send and receive data in remote locations, where only GPRS is available. Sometimes when its really bad you can still use SMS messages to send and receive data.