T-Mobile today announced it would allow subscribers to its "unlimited" calling plan to include family members for half price. Customers can add up to four additional lines to an unlimited plan for $49.99 per month each. Competitors charge full price for additional lines on unlimited plans.

Last February, Verizon Wireless unveiled a plan with unlimited nationwide calling for $99.99 per month and was quickly matched by competitors. T-Mobile's plan, which costs the same, also includes unlimited text, picture and instant messaging. Verizon charges $119.99 for that plan.

The introduction of unlimited plans initially depressed the stocks of carriers, but AT&T and Verizon have said that the plans actually increase their sales. More consumers upgrade to unlimited plans from cheaper plans than downgrade from older, more expensive plans.

"Mobile phones are a lifeline for busy families today, and T-Mobile wants to be right alongside them whether at home or on-the-go to help them stay connected," said Robert Dotson, president and CEO, T-Mobile USA. "This new unlimited calling and messaging plan for families delivers great value, and frees families to connect the way they want to for all their important relationships."

Since few customers use all the monthly minutes on their cheaper, limited plans, the unlimited plans are a good value only for a few percent of consumers. However the plans have become a major point of comparison and competition for the carriers.

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