The modem module we are currently using is a GSM/GPRS module - the SIMCOM SIM908. This is a quad band module, so compatible with everywhere. Very nice, and works well, but I am aware that the global cellular providers are moving away from 2G and long-term this may be a problem. The replacement SIMCOM module seems to be SIM5320. But, the frequencies seem more complex. Frustrating as we don't need the 3G speed - but we do need the frequency compatibility. http://wm.sim.com/producten.aspx?id=1029 There appear to be three variants of the module: SIM5320A Dual-Band UMTS/HSDPA 850/1900MHz Quad-Band GSM/GPRS/EDGE 850/900/1800/1900MHz * FCC * PTCRB SIM5320E Dual-Band UMTS/HSDPA 900/2100MHz Quad-Band GSM/GPRS/EDGE 850/900/1800/1900MHz * CE * GCF * ICACA SIM5320J Dual-Band UMTS/HSDPA 850(800)/2100MHz Quad-Band GSM/GPRS/EDGE 850/900/1800/1900MHz * Telec * JATE From the certifications, I'm guessing SIM5320A is USA and SIM5320E is Europe. There is also SIM5218, which appears to have similar features but is tri-band UMTS/HSPA850/1900/2100 or UMTS/HSPA 900/1900/2100 as well as GSM/GPRS/EDGE 850/900/1800/1900. It is more expensive and twice the size of the SIM5320. SIM5218A Tri-Band UMTS/HSPA850/1900/2100 MHz Quad-Band GSM/GPRS/EDGE 850/900/1800/1900 • CE • FCC • ROHS SIM5218E Tri-Band UMTS/HSPA 900/1900/2100MHz Quad-Band GSM/GPRS/EDGE 850/900/1800/1900 • CE • FCC • ROHS SIM5218C Single-Band UMTS 2100MHz Quad-Band GSM/GPRS/EDGE 850/900/1800/1900 SIM5218J Tri-Band UMTS/HSPA800/1900/2100 MHz Quad-Band GSM/GPRS/EDGE 850/900/1800/1900 • Telec • JATE From my limited research, it seems AT&T is using 850 and 1900, Three in UK is using 2100. Anyone know what the major carriers around the world use? What about the ones you are using now? Regards, Mark. P.S. By comparison, the iPhone5 is MTS/HSPA+/DC-HSDPA (850, 900, 1900, 2100 MHz); GSM/EDGE (850, 900, 1800, 1900 MHz); LTE (2 variants, with a few bands each).