Hi gel, I done excatly the same thing, bought a ipod touch, liked it so just got myself an iphone, I kept putting off getting one because of the price. Then I was going to wait for the new one, but just decided to get one today as I got it at what I thought was the right price.
12 month contract, £20 a month line rental, but £320 for the 16gb 3gs iphone. (you can get the 8gb for £222)
But the way I look at it, you pay £20 a month line rental (not bad 250 talk minutes, unlimited web and texts) Then at the end of the 12 months you can get the phone unlocked and sell it for about £400 and then get the newer one that has been out for a while and the price has dropped on that one then