In reply to ClimberEd:
I live in manorbier (5 miles west of tenby) and EE/Tmobile seems to get the best coverage around south pembrokeshire, which is lucky for me as that's what I'm on.
Even get a reasonable signal on cliff tops around St Govan's although it can be a bit patchy.
I would not rely on it as your only means of meeting up., especially on vodafone or 3.