I was able to get an AT&T Go Phone pre-paid SIM to work with the Telit GM862-GPS. As far as I can tell the cheapest way to go is to buy a $25 card so your money will not expire for 90 days, if you buy a $15 card the money expires in 30 days. I then added a 1MB MEdia net plan for $4.99. If you don't add a plan you have data access but they charge 0.01/1KB. So as far as I can tell $8.33/month is the cheapest I have found. Once you have a couple dozen units in service and are willing to sign a 1 year contract give Jasper Wireless a call, they are probably cheaper.