Hadn't been on this forum for a while, but wanted to point out that I've been using a FreedomPop Global SIM card for the past few months in my OVMS unit with no problems. It's a data only SIM card, so it won't send or receive SMS texts, but for getting the charge status, location, etc it works great. Best of all, the SIM is at most $10 to buy (usually on sale from $1-5), and has no further fees for the free 200MB/month level of service. Just be sure to CAREFULLY remove all of the "premium" features that are automatically turned on when you sign up for FreedomPop. It would be best to search online for detailed instructions on how to do this. Once you have it set up though, you never need to worry about paying for anything, you just get to check your charge status from anywhere.
If you already have a SIM in your OVMS unit, just reconfigure the APN to the FreedomPop settings, then drop in the new SIM. If you don't have your OVMS currently working, though, you may have to borrow a SIM, or else get a cheap H2O or other SIM just to do the initial setup.http://www.freedompop.com/worldwide
Actually, just after posting this I saw they're offering SIMs for $0.99 right now (with a free powerbank and selfie stick...) https://www.freedompop.com/offer/labordaysim
. Might pick up a third for myself. Why not?