i just emailed o2, response i got:
(only the bit in bold/italic is interesting)
Thanks for emailing us about the new iPhone 3G.
I've checked your account and I can see that you're currently eligible to upgrade your contract. Your current 12 month contract term will complete on 28 June 2008.
To upgrade your contract please call our upgrades team as our upgrades team deals with all the queries related to upgrades.
You can contact them free of charge on the following phone numbers:
1. 8001 313 136 from O2 phones.
2. 08001 313 136 from Fixed line phones.
3. 08706 007 102 from your O2 Pay Monthly phones. They're open:
-Monday to Saturday between 08:00am and 08:00pm.
-Sunday between 10:00am and 06:00pm.
Our upgrades team offers all upgrade deals and they'll be able to tell you about the various upgrade options available.
You don't need to visit the O2 store to activate the iphone you can activate your iphone via iTunes.
You can also register your interest to upgrade to the new iPhone 3G by using the link below:
http://iphone.o2.co.uk/registeryourinterest/
After you've registered your interests, we'll contact you in early July to tell you about the new 3G iPhone.
I hope you find this information useful and many thanks for your keen interest in the iPhone 3G.
Please visit our website using the link
www.o2.co.uk/iphone for the most up to date information on iPhone.
Should you need any information on our products and services, please visit our online Help Centre at:
http://www.o2.co.uk/help