USA mobile plans... It seems to be really complicated (or at least, phone provider websites are bad) to get a SIM-only, monthly rolling contract with minimal texts/minutes/data. Specifically on a network that will work with Fairphone (2G is fine, believe it or not). So I'm seriously considering not bothering. I started to worry about it being inconvenient/expensive for people with US numbers to call me, then had an epiphany. Making it more difficult for people to call me is a feature, not a bug.
I can call US numbers from Hangouts, and there are a million ways people can instant message me other than SMS. (FYI best results currently from Hangouts or Twitter, will probably make space for Viber again soon).