I haven't seen this phone this cheap for ages... And there is a strong chance It will be unlocked as it is on O2! The Sony Ericsson W300i is a walkman music phone, and (I think) comes with a 256mb card as part of the sales package. Might be the same price in store, but a cracking price nonetheless :)
"The Sony Ericsson W300i is a mid-range clamshell phone that brings the Walkman-branded phone range to the mass market. Sony Ericsson have shaved functionality off the phone in order to bring the cost down, but the core music function is top notch."