Viewers who get their television programs free, over-the-air and without a converter box will find themselves without service starting Friday, when the federally-mandated transition to an all-digital broadcast spectrum becomes final.

Those households - Nielsen Co. estimates about 2.8 million homes still aren't ready for the transition, while the National Association of Broadcasters says it's more like 2.1 million - will then become the focus of a scramble by broadcast stations, cable operators, satellite providers, telecommunications companies, retailers and policymakers to get them back to watching TV.

The affected households are likely concentrated in low-income, older and rural demographics. The market least ready, according to Nielsen, is Albuquerque-Santa Fe, where 7.6% of the households remain unready.

Industry watchers say some affected viewers will be motivated to buy a digital TV. The Consumer Electronics Association says TV sales are up about 32% in 2009 despite the recession, though lower prices are likely driving sales.

Others will buy a digital converter box for their old analog TV, and the government has launched a program to provide vouchers for up to two $40 coupons per household to help defray the cost; the program has been extended through July. Some, meanwhile, may simply stop watching TV altogether, while others may protest the change. Some level of public outcry is expected.

The cable, satellite and telecommunications industries are hoping that many disenfranchised viewers will bite the bullet and subscribe to a pay-TV service. A number of cable executives have said the transition provides a tailwind to their industry, which is struggling with a subscriber slowdown amid the recession.

"We've seen an increase in call activity in some markets as we ramp up for the transition," said Alana Davis, spokeswoman for Comcast Corp. (CMCSA).

Comcast, the nation's largest cable provider, has been particularly aggressive in advertising to those affected by the digital transition. Davis said the company has launched a "rapid-response team" to quickly deploy cable wiring and boxes in transitioning homes, and it is offering promotional deals such as free basic video service for a year with a subscription to its phone or Internet service offerings.

Cablevision Systems Corp. (CVC), Time Warner Cable Inc. (TWC), Verizon Communications Inc. (VZ) and AT&T Corp. (T) also have targeted those affected by the transition and have worked to assure their existing customers that they won't be affected by the switch.

Satellite-TV companies have reported muted impact in the lead-up to the transition.

"I think, clearly, the digital transition was a positive," DirecTV Group Inc. (DTV) Chief Executive Chase Carey said during an investor conference last month. "I think it's really tough to quantify how big a one. I don't think it was a major positive."

Dish Network Corp. (DISH), however, didn't see much benefit. CEO Charles Ergen said during the company's quarterly conference call last month that its competitors likely benefited more because Dish's marketing effort hadn't been as strong in recent months. He said there was no material impact from the transition.

The next few months and the ensuing financial reports from the industry will shed more light on the opportunity posed to pay-TV by the transition, and its effects in the market will continue to play out after the deadline.

Hudson Square Research analyst Jeffrey Wlodarczak said the transition could be "a larger-than-expected driver" for cable and satellite stocks, given the low valuations in the sector, though he forecasts a decline in net new video subscriber additions for the industry of 20% in the second quarter.

Wlodarczak recommends shares of DirecTV, Dish, Liberty Entertainment (LMDIA),Time Warner Cable and Comcast.

For their part, broadcasters downplayed the significance of the event privately and directed inquiries for this story to the National Association of Broadcasters, which says 82% of U.S. households relying exclusively on antennas to watch TV are fully prepared for the switch.

The broadcast industry is already reeling from the drop in ad markets because of the recession, particularly in local media markets. Any loss of viewers stemming from the transition will only add to their woes.

The federal government delayed the transition, which was originally set for February, as millions of households were estimated to be unprepared. Since then, Nielsen estimates the number of unprepared households has been cut in half due to public awareness efforts by broadcasters and government agencies.

-By Nat Worden, Dow Jones Newswires; 201-938-5216; nat.worden@dowjones.com

(Roger Cheng contributed to this report.)