I believe, depending on the SIM provider that the SIM (as long as the voltages are correct) will work with most modems, but the modem will only negotiate at the speed it's cellular interface allows, be it 2G or 3G (or even 4G now), 3G can fall back to 2G, but 2G won't fall forward, meaning that if a SIM is 3G, it should work fine with a 2G, bit if it's a 2G only SIM (would be VERY rare these days), it probably won't work with a 3G modem.