But the largest U.S. cable company, which sources have said is in talks to take control of NBC Universal, suffered from a lack of corresponding gains in revenue received from each customer, due to promotional discounting to woo or retain subscribers.

"While third quarter unit growth showed some cause for cautious fundamental optimism, we are wary of increased competition and maturation," said Standard & Poor's Equity Research analyst Tuna Amobi, who rates Comcast shares at "strong sell."

The Philadelphia-based company reported 361,000 new high-speed Internet customers and 375,000 new digital phone subscribers in the third quarter, offsetting the net loss of 132,000 basic video subscribers.

Barclays Capital had expected 310,000 voice and 320,000 Internet additions.

But Collins Stewart analyst Thomas Eagan said, "They didn't generate the revenue and cash flow that we had expected."

On a conference call with analysts, Brian Roberts, Comcast's chief executive, addressed reports about NBC Universal talks. But he shed little light on the existence of a potential deal.

"While we can't comment on rumors, I would like to reinforce that we only look at opportunities in our core businesses that potentially can accelerate growth, make those businesses more profitable and differentiated and give them the benefits of scale," he said on a conference call.

According to sources, Comcast would inject $4 billion to $6 billion of cash and its cable networks into a joint venture with NBC Universal's parent General Electric Co, creating a content powerhouse spanning broadcast and cable TV, movies and theme parks.

The company's third-quarter net profit rose to $944 million, or 33 cents a share, from $771 million, or 26 cents a share, a year earlier.

Excluding special items, including income tax benefits and financing expenses, the profit was 28 cents a share, outpacing analysts expectations of 25 cents a share, according to Thomson Reuters I/B/E/S.

Revenue rose 3 percent to $8.80 billion, just shy of analysts view of $8.85 billion.

Free cash flow -- a measure of cash left after all expenses are paid for the quarter -- rose nearly 20 percent to $1.11 billion.

Shares of Comcast were down 29 cents to $14.22 in afternoon Nasdaq trading.

(Editing by Derek Caney, Dave Zimmerman)