I am with O2, and on Saturday I called them to discuss upgrading. They confirmed that I could pay a £160 'fast-track upgrade' fee to get the 4S at the subsidised price. It worked out cheaper than buying a 4S sim free, so my plan was sorted. Today I went to the Liverpool O2 store that I was planning to get my 4S from, just to check that what I was told on the phone was true. Well well well... Apparently lots of people are trying to do the same as me, and O2 are worried they will run out of stock. They have silently introduced a new policy - you won't be able to upgrade this Friday unless you are on a contract costing more than £40 per month (mine is £37). They aren't announcing the change so I think a lot of o2 customers will be very disappointed on Friday. I went to the Apple store, and they confirmed after checking my eligibility that I was no longer able to upgrade because o2 had pulled their existing offer. Looks like I'll be buying a sim free phone... Long story short: If you are on o2 and want a 4S on launch day, you won't be able to upgrade unless your contract costs more than £40 per month. Your only alternative is to wait a few weeks for O2 to change its policy back, or buy a 4S sim free from the Apple store.