MetroPCS is trying to get its customers to cut the cord entirely and has launched a landline-replacement service.

The GroupLine service lets up to five MetroPCS subscribers receive calls on a shared number while still retaining their individual numbers. Users can call the GroupLine number and reach all subscribers on the plan simultaneously, and there's also shared voice mail. The service is priced at $5 a month for subscribers with a MetroPCS family plan.

"GroupLine was developed with families' needs in mind," Roger Linquist, CEO of MetroPCS, said in a statement. "We are all on the go, and we often have news to share with the whole family. With GroupLine, instead of making numerous calls, everyone can be reached at one time."

The move comes as MetroPCS appears to be one of the few in the mobile industry benefiting from the economic downturn. Cost-conscious customers aren't yet willing to give up their cell phone service, but some are leaving AT&T, Sprint Nextel, T-Mobile, and Verizon Wireless for the likes of prepaid providers like MetroPCS, Cricket, and Virgin Mobile. These companies offer unlimited voice and text plans for about $40 a month with no credit checks or long-term contracts.

For the first quarter, MetroPCS added about 684,000 new subscribers, which is the highest quarterly growth in the company's history. This represents a 59% year-over-year increase, and the company now has more than 1.5 million subscribers.

"Our continued growth in a slowing economy is a result of our innovative unlimited wireless service offerings that are predictable, affordable, and flexible, providing subscribers with a superior value proposition," said Linquist.

It's unclear if this growth is sustainable, though, as some subscribers may flee to the larger carriers once the economy rebounds. One area of concern for MetroPCS is that the first-quarter rate at which subscribers leave, known as "churn," was higher than the same period last year.

Most companies are just starting the hard work of mobilizing workforces by bringing the software they use to smartphones. InformationWeek analyzed this issue in an independent report, and it can be downloaded here (registration required).