I'm NOT a lawyer, but
if the original contract gives them the right to make unilateral changes to the T&Cs then they might be on sounder ground.

If you were able to convince them that you were within your rights to drop out of the contract, then you'd be needing to restore them to the position they were in if the contract hadn't existed, e.g., you'd have to return the handset in unused condition.
(Eds Meds Mathskillz=1,Socialskillz=0, Fri 29 May 2009, 10:49, 1 reply, 16 years ago)

Relevant verbage from the contract
7.2.3. A Cancellation Charge won’t apply if You are within the Minimum term and:
7.2.3.1. Our entitlement to operate the Network ends at any time; or
7.2.3.2. You are a Consumer and the change that We gave You Written Notice of in point 2.11.2 or 7.1.4 above is of material detriment to You and You give Us notice to immediately cancel this Agreement before the change takes effect;
(b3tamax Mate, you're fat and I'll throw you in the river, Fri 29 May 2009, 10:56, Reply)

Hmm
If 7.2.3.2 is in your contract I'd suggest getting on the blower to the mobile phone company and suggest that they shove their contract, sideways, with the assistance of a blast of compressed air.
(Eds Meds Mathskillz=1,Socialskillz=0, Fri 29 May 2009, 10:58, Reply)