Wall Street saw a crushing threat looming for MetroPCS ( PCS) as low-end rival TracFone -- a big player in Wal-Mart ( WMT) and 7-Eleven stores -- rolled out an unlimited calling plan.

The rumor had it that MetroPCS and prepaid peer Leap Wireless ( LEAP) customers, unencumbered by contracts, would flee to TracFone's unlimited $45 Straight Talk offer.

But some now say the Tracfone stuff may be a lot weaker than anticipated.

For those unfamiliar with the full landscape of our nation's great mobile phone addiction, you should know that we are a two-class wireless society.

One class is the conventional contract customer who buys fancy telco-subsidized phones like Research In Motion ( RIMM) BlackBerries and Apple ( RIMM) iPhones, and makes regular monthly payments north of $50 a month.

The other group, known as prepaid, consists of customers who pay full price for cheap phones and refill their minutes allotments as needed.

MetroPCS and Leap have become the low-cost cell phone alternatives serving small cities and towns outside the prime big-city focus of giants like Verizon ( VZ) and AT&T ( T). The prepaid offer has a strong appeal for people lacking strong credit histories. It also is a cheap wireless alternative to those looking to cut the home landline.

Prepaid's appeal has cranked up in the past year as unlimited calling and messaging offers have gained popularity.

For a $45 unlimited prepaid calling purchase, users get an all-you-can-eat supply for 30 days. And not only is it an easy fix for heavy callers, it's also a big stimulant for growth among the prepaid companies.

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