I have been using my fairphone for about 10 months with a three Sim card, then at the beginning of july 2015, my fairphone could not longer receive signal with my fairphone (FP1, second production run).
Other sim cards still work in my fairphone, and my sim card works fine in other phones (including a fairphone 1, first production run).
Has anyone else with this fairphone in the UK been using three and had similar problems?
I’m neither in the UK nor do I have a 3 SIM card, but: Have you checked your APN settings? Sometimes providers change their settings without notifying their customers (at least not the SIM-only-customers ).
3UK only provides 3G connections (i.e. no 2G). The Fairphone1 allows 3G on only one of the SIM slots, though you can choose which one. It may be worth double-checking the 3G settings. You can find this under Settings > [Wireless & Networks] More… > Mobile Networks > 3G service.