UPDATE 2-Sprint beats on quarterly revenue, raises outlook; shares jump

(Adds analyst comments, detail on adjusted earnings per share)

NEW YORK, Feb 2 (Reuters) - Sprint Corp reported quarterly revenue on Friday that beat analyst estimates, as the No. 4 U.S. wireless carrier raised its free cash flow outlook for the 2017 fiscal year.

The company has sought to strengthen its balance sheet by cutting costs and mortgaging a portion of its airwaves and equipment, but industry analysts have raised concerns about how it can adequately fund network improvements.

Sprint now expects $2.5 billion to $2.7 billion in operating income, up from its previous estimate of $2.1 billion to $2.5 billion. It expects adjusted free cash flow of $500 million to $700 million, compared to previous estimates of breaking even.

Shares jumped 4.9 percent to $5.35 in premarket trading.

The company reported net additions of 184,000 phone subscribers who pay a monthly bill in the quarter, compared to additions of 368,000 a year earlier.

"Volumes came in surprisingly strong while profitability and cash flow were also better," analysts at Jefferies said in a note.

Net operating revenue in the third quarter ended Dec. 31 was $8.24 billion, down from $8.55 billion a year earlier.

Sprint reported quarterly net income of $7.16 billion, or $1.79 per share, due to the impact of federal tax reforms, after a loss of $479 million, or 12 cents per share, a year earlier.

Excluding the impact of tax cuts signed into law by U.S. President Donald Trump late last year, net income was 3 cents a share.

According to Thomson Reuters I/B/E/S, analysts had expected revenue of $8.15 billion and a net loss of 4 cents a share. (Reporting by Anjali Athavaley; Editing by Bernadette Baum)