By PETER SVENSSON Sprint Nextel Corp.'s subscriber losses slowed in the fourth quarter, an encouraging sign for a wireless carrier that has lost millions of customers over the past few years.Sprint lost a net 148,000 subscribers in the last three months of 2009, far fewer than the 545,000 who fled in the third quarter, the carrier said Wednesday.Sprint reported a quarterly loss of $980 million, or 34 cents per share, for the last three months of 2009.