T-Mobile USA on Wednesday hoped to increase competition with the launch of a new unlimited family plan it hopes will lure subscribers to rival carriers. The service requires T-Mobile's existing unlimited individual plan but halves the price of unlimited access for each family member that signs on; each extra line costs $50 to add the same unlimited national calling and messaging services (including instant messaging) as the parent account.

Plans can be added effective immediately, T-Mobile says.

The change signals a renewed level of competition in US cellular access. While four out of the top five cell carriers all offer unlimited phone plans, most focus almost exclusively on individual users and only offer slight discounts on multiple users on the same account. Sprint's Simply Everything plan, as an example, drops the price for extra lines by just $5 each.