I was in the same situation as you mate. I couldn't get any prices over the phone or webchat, however the MPD run Nokia stores quoted me at around £130 for an upgrade on a £35pm, 18month contract, oh and at least a weeks-10 days wait. Expect maybe £30 cheaper online, at a guess?

I gave up with MPD after 3 weeks of getting messed around after giving them my number and being told I was on a "reserver" list with the web orders, and they'd call me when they got stock...they then bumped me to the back of the queue and said they'd call after all the web orders - even the ones placed after I "reserved" mine - were fulfilled.

Today I ordered from Nokia flagship Regent St who said they had stock, could ship today and offered me an upgrade on the same tariff for £90 up front- all done over the phone and posted out.

I hope that helps.