Do what I did. I found the phone I wanted - but it was on a different provider (Orange and I'm o2). Popped along to the local independent mobile phone shopped and had it unlocked for about a tenner.
Then, being totally you-know-what retentive, I found a shop on the www that could de-brand it, so the original Orange logo and facilities/selections were reset to 'normal'. That too was about a tenner and I had the phone back by return of post.
But... I got a very nice phone at the end of it.
Nearly anything is possible - but it just needs to be what you want and at a price you're willing to pay.