This is directly from the Cingular contracts: 'If we increase the price of any of the services to which you subscribe, you may terminate this agreement without paying an early termination fee, provided your notice of termination is delivered to us within 30 days.' it means you can cancell your contract with Cingular if you give them notice within 30 days without paying any termination fee.
That clause does not apply to any features/options that are paid in addition to the contracted service. It would only apply if, for instance, you had a contract for $60/month for 1500 minutes and they raised the charge to $65/month for the same 1500 minutes and forced you to pay the new rate. Since you pay separately for N&W, message packages, insurance, etc, those items are not affected by the 'adverse material change' clause.