Hi, it's not really what you were asking, but I noticed you mentioned 'upgrading' your phone. In nearly all cases you are much better off getting a new deal altogether, you can get a free phone, cashback and free gifts, you nearly always get a much better deal than just upgrading. You can also keep the same mobile phone number if you change networks. Have a look at this website, I've found some great deals on there which carphone warehouse (who i got my phone with last year) just cannot match for an upgrade:
www.dialaphone.co.uk