I dont think bad signal is a good argument as now days all operators have a coverage map on there websites and fob you off with a "you should have checked before you bought"

Your best bet would be to keep the phone for now and then maybe purchase some insurance in a few months when the n900 is discontinued. smash it and then they will have to replace for a similar phone...

A question i asked in a another thread is where would one stand if nokia do not have flash 10.1 on the n900, would this void the contract as you whent for a flash phone that no longer supports flash?