My phone kept losing signal intermittently so phones4u replaced it with a seemingly mint model (no stickers on it though) and...it's so much worse! I am livid.
The symptoms are intermittent bad 3g/HSDPA (webpage timeouts etc) then loss of 3g/HSDPA connection (the symbol at the top next to the signal bar vanishes) then in settings mobile data
says 'disconnected because service is unavailable' (screenshot to follow). Disabling/reenabling mobile data/airplane mode/rebooting doesn't resolve this - it just comes back and as when.
Unlike my previous One which seemed to also lose signal i.e. I couldn't make calls and I got a x on the signal strength, this appears to only be the mobile internet.