Because the tariff I am on with T-Mobile isn't available anymore and I don't want to lose it. I want to use an iPhone on this tariff is the long and short of it. I pay £25 a month for £60 of usage from my phone - no limit on calls, texts etc other than total usage costs are within £60 - which they 99% of the time are. Then I get Web n Walk for another £7.50, totalling £32.50 a month. The closest match to that from o2 is £35 amonth (600mins, 500texts, plus free mobile data) However, by not taking a "hard upgrade" (ie, upgrading to a new phone) I get a £10 a month line rental discount, dropping my monthly bill to £22.50. £22.50 x 18 = £405, whereas £35 x 18 = £630.

So, to work out total expenditure, if I was to cancel my T-Mobile contract, and take out a new one with o2 + pay £100 for the iPhone, I'd be looking at £450 (£350 to cancel T-Mombile + £100 iPhone) and another £225 over the course of the contract term, totalling £675 in extra charges.

So, to sum up, all I have to do is get an iPhone, from somewhere like Greece or Italy (where local laws dictate all phones must be sold unlocked to be used on any network) for less that £675 and I'm all set For this year the price will be the same as if I am had cancelled T-Mobile, signed to o2 and bought the iPhone, but after this year, I'm on a winner....

Only thing is, I have to find a) a proper Apple unlocked iPhone, and b) £675