He decided to go with the low-cost SIM800L GSM modem, but as it only works on 2G networks, provisions have been made in the board design to swap it out for a more modern module should you desire.
The shield is based around the SIM900 GSM/GPRS radio module, and is compatible with the SIM908 GSM/GPRS module that adds a GPS receiver. Also on board this shield are a pair of 1/8″ audio ...