Sprint prepaid brand No. 4 coming to a Walmart near you

Sprint’s mystery fourth prepaid brand now has a name and an official retailer. Sprint (NYSE:S) today revealed that its pay-by-the-minute prepaid service will be called "Common Cents Mobile" and will be sold within the confines of Wal-Mart’s (NYSE:WMT) retail empire.

Common Cents will have flat rate pricing of seven cents a voice minute and seven cents a text message, but Sprint is adding a twist to distinguish itself from other pay-per-minute operators. It’s introducing a billing method called Round Down, which counts only the last full minute used in a call against a customer’s minute allotment. Other operators typically round up to the full minute, billing two minutes for a one-minute and 20-second call, for instance. Sprint, however, isn’t going so far as to comp every phone call under a minute in length, though. Round Down only goes into effect after the first minute.

The minutes will expire just like other pay-by-the-minute services. Sprint will offer them in two denominations: $20 for 565 minutes good for a month and $30 for 848 minutes good for 60 days. The phones are as inexpensive as CDMA devices can reasonably be. It will sell a bare-bones LG Electronics handset for less than $20, a Samsung device for $40 and Kyocera handset for $70. The higher-end devices will have some data capabilities, which Sprint will sell for $1 a MB per day. And while a text message effectively deducts a minute of talk time from a customer’s account, Sprint is also making an unlimited monthly SMS plan available for $20 a month.

Sprint announced last week that it was overhauling its prepaid brands in an effort to capture every possible segment of the growing prepaid market. Virgin Mobile emerged as its higher end, young and tech-savvy brand, which also included its prepaid mobile broadband plans. Boost remained geared at the big middle, and while offering data options appeared to focus on the all-the-you-can-eat prepaid segment. On the lower end, Sprint positioned Assurance as the brand for low-income customers, many of whom qualify for government assistance.

Common Cents seems to fall somewhere in the middle, targeting people on a budget who want to carefully manage their wireless consumption, but providing options for more services. Sprint estimates it will be its biggest potential market in terms of customers, though, citing Nielsen statistics that 63% of the prepaid market is pay-by-the-minute.

Common Cents phones and prepaid cards will go on sale on Saturday at 700 Wal-Mart stores, which at least initially have an exclusive. Sprint did not say whether it would expand into retail channels beyond Wal-Mart, but the fact that the service won’t carry the Wal-Mart brand is indicative that it probably will.