Like I said in that other post Orange and T-Mobile cover 97% whilst Vodafone and O2 cover 99% of the UK population.
I dont think Orange or T-Mobile have any intentions as yet in improving 2G coverage in remote areas, complain and then they might do something about it!
You might find this hidden section of the Orange website useful???
http://www1.orange.co.uk/about/phone_masts/index.html