I live in the UK now but spend about 15 weeks a year in the US (largely the SF Bay Area) and I'm looking for some options to keep using my phone and data services without paying through the nose. For reference, I have an iphone 5 on o2.
I've looked into Karma (https://yourkarma.com/) which looks like a neat service.
I've also looked at getting a US sim but then I worry about imessage, what'sapp etc not working.
I'd love to hear what's worked for you and what you'd recommend.