Cingular Wireless is set to increase its fee for text messages from 10 cents to 15 cents, effective January 21 of next year. Cingular will use the increased fee as a way to encourage subscribers to sign up for a bulk SMS plan. The carrier's hike only affects subscribers who do not subscribe to a bulk SMS plan. The affected subscribers are eligible to cancel their contract with Cingular without an early termination fee, since the contract specifically provides that loophole when rates increase for any service. Sprint made the same increase for SMS rates in October, but did not disclose how many subscribers left as a result. T-Mobile and Verizon Wireless still charge 10 cents per SMS, but it's likely the two will raise that rate next year. Their ARPU's may depend on it.