Contractual Obligations: Are you in a position to upgrade?

First off, I'll point out that I live in the UK and although my understanding of US phone contracts is pretty much limited to what I have heard the guys on The Vergecast discussing, I happily welcome contributions to this post from everyone on the other side of the pond as I have a strange nerdy fascination/FOMO on what carriers in other countries offer (probably a case of "grass is always greener" but there you go).

Currently, I have an iPhone 4S 64GB. I am on a 12 month contract with O2 - which expires at the end of September - and I pay £31 (about $50) for unlimited calls, texts and 1GB of data per month.

When Apple announced their press conference for the 12th, I immediately went onto the O2 website and submitted my iPhone for the recycling process which currently lists my model as being worth £325 (around $520). Although this may seem a little premature, you can guarantee that this price will plummet as soon as the new iPhone is actually announced next Wednesday and, seeing as O2 allows a 14 day grace period for the receipt of the old phone, I figure that at worst I'm going to be phone-less for no more than 4 days.

Assuming that the new iPhone (you'll notice that I am flatly refusing to refer to this thing as the "iPhone5" - urgh) is priced similarly to the 4S, then I should be able to upgrade on launch day to the top-end model for about £30 (after subtracting my 4S rebate) whilst also keeping myself on a 12 month contract.

This, I think, puts me in a pretty good position compared to a lot of folks out there. I'm interested to hear what other people expect to pay for upgrading and what people are paying now. If you aren't planning on getting the new iPhone at launch, then is it due to contractual obligations?