Open-electronics have introduced new version of their Arduino GSM shield. The new shield uses well known GSM/GPRS module SIM900 and SIM908 GPS module what makes it versatile for voice and data communications.
The new module has better power supply solutions and offers more customizations and configurations. All you need is to attach microphone and headphones in order to make phone-calls with Arduino. As usually there are libraries available for running your applications in shortest time possible. Couple Arduino sketch examples will make this happen even faster.