NEW YORK » Sprint is introducing a new wireless plan that guarantees new and existing subscribers unlimited voice, text and data plans in a move to differentiate its service from rivals AT&T and Verizon.

Sprint Nextel Corp. says that the plan, called the "Sprint Unlimited Guarantee," offers unlimited data for $30 a month on smartphones and $10 per month on traditional phones. Voice and text cost $50 for the first line and less for additional phone lines.

Sprint, the third-largest U.S. wireless carrier, is now under the control of Japanese investment firm SoftBank. Softbank owns a 78 percent stake in Sprint after a $21.6 billion deal closed on Wednesday.

Both AT&T Inc. and Verizon Wireless have ditched unlimited data offerings to new customers.