Sprint Nextel Corp. (S) said Thursday it will begin selling a prepaid cell phone service at Wal-Mart Stores (WMT) beginning Saturday.

The plan will charge users 7 cents per minute for phone usage and the same amount per text message.  The new plan includes Sprint's new "round down" feature in which calls will be rounded down to the nearest minute rather than up.

While other contract plans have continued to lose customers, prepaid wireless has been a bright spot as customers try to hold down costs.

Shares of Sprint Nextel were up 7% in Thursday afternoon trading.  Shares of Wal-Mart rose about 0.5%.