I'm living in London for three months this summer for an internship and want to keep my smartphone capabilities. I have an ATT GS3, and I'm assuming that's GSM and capable of working on any GSM SIM card? Has anyone purchased an international prepaid SIM card with data? Looking for specific networks that offer a usable amount of data, voice and SMS. I think the ATT option is a total ripoff, so this seems like the best plan.