Boost Mobile, the MVNO running on Sprint’s smaller Nextel network, is offering the most aggressive national unlimited plan yet—for $50, customers will get an unlimited voice, texting, Web access and push-to-talk services, AP reports. The kicker is that it is available without a contract. Other regional players such as MetroPCS and Leap offer plans that cost about $45 to $50, but are limited geographically. Most nationwide carriers offer unlimited plans for $100 a month, and Virgin Mobile USA (NYSE: VM), which runs on the Sprint (NYSE: S) network, offers an $80 unlimited plan. The new pricing beats Boost’s cheapest plan by $20.

It’s likely that Boost, which is a wholly owned subsidiary of Sprint’s, is feeling pressure from its parent to perform since Sprint has had a hard time recruiting and retaining customers. In recent weeks, Sprint has provided additional incentive to Virgin Mobile to add more subscribers. Boost had 3.9 million customers at the end of Q3, and Virgin Mobile had 5.38 million at the end of the year. Matt Carter, Boost’s president, told AP the offer could appeal to even the higher-end postpaid subscribers who want to save money and don’t mind the small range of handsets or don’t want premium services such as streaming video or music downloads. At the same time, Virgin Mobile, which was focused exclusively on the pre-paid market, is moving upstream with the purchase of Helio.