The other day it came to my attention that the latest version of my mobile contract (T-mobile solo 30-day, £20pm, 500mins, unltd texts) now featured an extra 100 minutes and free unlimited internet for people who were starting a new contract. So I phoned up T-mobile, nicely asked them to move me on to this new deal, and they promptly charged me 25p for the honour of telling me, for some reason or another, that they couldn't.
So the next day I phoned them up, told them I had every intention to moving to Vodafone's 30-day contract, and they put the extra minutes and free internet on immediately :P
I can highly recommend these 30-day contracts for people who have their own (not network locked, unless you use the same network) phones already - as they don't rip you off for a phone with it, you get a better deal. The current T-mobile solo 20 plan is on offer and looking good - for £20 you get 600 mins, unlimited texts and free internet on your phone, which you could easily pay £40 for on other networks or with a handset included.