Signed up for this mobile service and like it so far. fi.google.com $20 per month for unlimited calling and text within the US (and maybe other countries). No SIM card required. Works internationally. International call rates depend on where you are at but SMS to any number is unlimited and free in 135 countries. Data rates are a bit pricey at $10/GB but it is a nice feature as it automatically connects to the fastest available network in whatever country you are in. So far I know that it works in the US, Canada, Russia and China (got a message welcoming me to those countries as I flew over them). I suspect the only countries it doesn't work in are countries that most people have no interest in visiting. I think it only works on newer (expensive) phones. Not sure what will happen once I put in my Afghan SIM card when I get back to work but I'm hoping it acts like a dual SIM phone.