@stamenkd

Under distance selling regulations, you can return the phone within 7 days without reason but it would have to have been unused. You could then get a different phone on the existing contract.

If you put the SIM in though, you've activated the contract - and under their returns policy, you have 7 days to cancel the contract, but you can not do this if you've used the SIM at all...

After the 7 day window (for faults), you deal direct with Nokia. This isn't usually a bad process, but its NO Apple! You take it to a repair centre or Nokia approved store (my local Vodafone store is one of these and many Carphone Warehouses are). They will send the phone back to Nokia for you and have it repaired or replaced if needs be. This isn't a bad experience - done it several times with my N73 and once with my N96. They have a good turnaround time. Problem is, with a shortage of N900's at the moment, you'd probably have a long wait to get a replacement!