Three UK (Hutchison) also let you upgrade 3 months before the end of the contract I believe, and downgrade on payment of a relatively small fee after you have passed some threshold in your contract time.

But then, if you timed it right and were lucky like me, you ended up on a £10/mo SIM-only 1 month(!) contract with "unlimited" data (3GB/mo), "unlimited" texts (3000/mo), "unlimited" 3-to-3 calls (2000 minutes/mo), network-assisted Skype, and 300 included minutes to other networks & landlines.

Perfect for my new N900 when it arrives. I have the SIM waiting and ready and really hope Nokia's team have the 3 SIM problem fixed by then :-)

It's a pity the 3 signal is so (ahem) variable, disappearing often, and with deep shadows all over the place, even in a town (Oxford) which is supposedly "very good" coverage.

A 3 shop salesperson told me they are combining infrastructure with T-mobile over the next year, which should greatly improve the coverage and shadow situation.