As far as I know of, this is a Vodafone specific phone and, even though it can be unlocked, it still won't accept non-Vodafone SIM cards.
I had the Vodafone 810 and gave it to a friend six months later (as I got annoyed with the keypad) and he wanted it unlocked to use with his O2 SIM, but even though it was unlocked, it would still not accept his O2 SIM card.
However, the ASDA Mobile network uses the Vodafone signal, so if you want to move networks to Asda, that will work.
Electric Dragon, March 2009