In reply to climbercool:
I'm on EE and their 4G coverage is suprisingly good in a lot of parts or south pembrokeshire, where I live. I also had good coverage on Arran last year and the Outer hebridies the previous year. Good enough to watch tour de france coverage in some seemingly pretty remote spots when wild camping along the hebredian way.
You can always get a no signal zone in an area of otherwise good coverage though, as you can in cities.
I stayed on a site with Wi-Fi in cornwall 5 years ago, I imagine this might be quite common among posher sites now?