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.

This tasty proof-of-concept cellular sandwich is made by adding a Sim900 GSM/GPRS module, which communicates ... He’s powering it with a LiPo battery and using a DC-to-DC converter to set ...