Yes it can be unlocked. If you get it done at the shop, get them to debrand it in with the deal.
DIY, have a google for SEKING. Works most of the time without problems....If there are any issues then take it to the shop anyway...will just need a reflash and unlocking.
Some places charging £15 - £20 now, have a hunt round.
Only real way I'm afraid...Debranding is quite important on the SE's, as 3's firmware is shite.