Comcast, already the largest U.S. cable television operator with 24 million subscribers, says it’s now the fourth largest U.S. residential phone service provider, too.

Chief Executive Brian Roberts is telling the Consumer Electronics Show audience that his company has made that mark less than three years after it started touting its digital voice service. 

Comcast can’t officially give us an exact number of phone customers until it publishes its fourth quarter results at the end of the month. But a source close to the company points to the fact Comcast had 4.1 million phone subscribers at the end of the third quarter and has been growing at a pace north of 500,000 a quarter for the last few periods.

This is important from Comcast’s perspective not just for bragging rights but because market perception is that the phone companies are winning the battle of convergence with their new advanced video services.

Back in November Wall Street research analysts at Oppenheimer & Co. pointed out that in the third quarter U.S. cable operators lost 185,000, or 2 percent of their TV subscribers, while the phone companies added 277,000.

But the cable companies, led by Comcast, added 1.2 million phone subscribers while the phone companies lost 1.146 million of their core residential landline customers.

Yet even while Comcast wins this battle it may be losing the financial war. Its shares have plunged 40 percent since the end of January 2007, while AT&T and Verizon were two of the best performing stocks in 2007, up 13 percent and 14 percent respectively over the same period.

(Photo: Reuters/Comcast CEO Brian Roberts)