SIM800 modem

Technical specifications:
GSM/GPRS/EDGE 850/900/1800/1900MHz
Controlled by AT commands (3GPP TS 27.007, 27.005 SIMCOM enhanced AT Commands)
Automatic baud rate detection for AT commands
Send and receive GPRS data (TCP/IP, HTTP, etc.)
Maximum GPRS data transfer rate: 85.6 Kbaud
Encoding: CS-1, CS-2, CS-3 and CS-4
Supports GSM 07.10 protocol
Supports SIM cards with 3V and 1.8V power supply
Supply voltage: 3.4 ... 4.4 V (nominal 4V)

An RJ-45 connector is integrated on the modem board, which allows connecting an external audio device.