T-Mobile have followed suite after O2 and Orange on this click the link to read the forum thread for more information
From 1st June all 07744/55 calls will be charged, if this was done within your contractual period, afaik you are no longer tied to the contract due to the change....
Sorry, considering past instances of things like this I should of mentioned, it REALLY helps if you used these numbers in the past as it proves a detrimental change to your contract usage.
Although really it is a change of T&C within the contractual period nonetheless, what you can blag however is what the forums are for however and hopefully people will provide useful information.
Title is somewhat misleading. Doesn't look like anyone's been successful in cancelling contract.