Sprint Nextel Corp's quarterly revenue rose 6 percent and it added mobile subscribers for the first quarter in more than three years, sending its shares up 3.4 percent in premarket trading.

The No. 3 U.S. mobile service added 58,000 contract customers in the quarter, ahead of the average expectation for almost 17,000 customer additions from eight analysts contacted by Reuters.

While the customer number was tiny compared with growth at bigger rivals Verizon Wireless and AT&T Inc, it marked a milestone for Sprint, which last reported contract customer growth in the second quarter of 2007.

Sprint expects to report contract customer additions for the full year 2011, marking the first full year of subscriber additions since 2006.

Some analysts have said however that Sprint may revert to subscriber losses in the current quarter as Verizon Wireless launches the Apple Inc iPhone. The venture of Verizon Communications and Vodafone Group Plc , started selling iPhone in its stores at the same time on Thursday as Sprint reported its earnings.

Sprint's loss narrowed slightly to $929 million, or 31 cents per share, in the fourth quarter from $980 million, or 34 cents per share, a year earlier.

Revenue rose to $8.3 billion from $7.87 billion and exceeded the analysts' average estimate of $8.15 billion according to Thomson Reuters I/B/E/S.

Sprint said 2011 capital spending would be about $3 billion and it expects to continue to generate free cash flow in 2011. Free cash flow refers to profit excluding amortization and depreciation, but including capital expenditures.

Sprint shares were up 15 cents at $4.50 in premarket trading.

(Reporting by Sinead Carew; editing by Lisa Von Ahn and Derek Caney)