I found cell reception to be alarmingly bad in the UK outside of populated areas. Entire stretches in Wales with no coverage. Days on 3G (if you're lucky!)

Iceland had stunningly good coverage; no matter how remote you were, it seemed like full service everywhere. (granted, I did't cross the center of the island).

Had no cell coverage on the Rallarvegen in Norway, which surprised me.

But yeah, it's all nothing like the US.