Id agree to move away from traditional landlines, but only if the problem was the connectivity. I dont think this is the issue as the download speeds reported are quite good. I would still suggest its just the provider.
3G seems a bit odd though as these (in my limited experience) have been a bit pants - way slow, tempremental connection and high cost (esp if you go over your download limit).
Maybe thats just Northern Ireland though - we are a bit behind the times!