This may or may not work for you but worth a try. When I've been on Voda in the past in poor coverage areas they tend to have a better 2G signal. If there is a way to disable 3g on your handset you may find you get adequate coverage for your needs. I realise this is not ideal but worth a go while you figure out long term the best solution.
Been a bit busy today but have a few things to respond to. First we're in Viewmont Drive, Harbour View - which is quite ironic because the only view we get is from tiptoe from the roof (which we don't venture onto very often).
I'd be quite hapy with just 2G but the phone that seems to standout for reception (according to the consumer test - hadn't realised it had this info even if not readily useable) is the Sony Xperia P. According to Consumer it's streets ahead of everything else.
So we might have to consider this - although they're quite dear (not like the flashy phone leaders) and worst of all, gui driven. I confess to being old-fashioned - made worse by the fact that I had a stroke caused by a previously undiagnosed hereditary condition. So I've avoided touch screens - my Kindle is one of the old fashioned ones, and I don't see the merits of Windows 8 (but then again I rubbished my mate for getting one of the first Mac's way back).
It looks like I'll have to get my hands on one - but I've not seen one in the local Vodafone outlet. I know Sony had their Kindle equivalent limited just to Sony outlets at first - don't know the current situation - but I assume their cell phones aren't limited to Sony stores.