SAN FRANCISCO - Having already equipped most adults and half of all teenagers with cell phones, the mobile phone industry is now turning its attention to the last untapped demographic - people over 65.

But its dreams of collecting monthly subscription fees from grandparents talking to their grandchildren, retirees calling friends from their recreational vehicles or checking in with their doctors may exact a hefty and unexpected price. The mobile phone industry has roused the interest of AARP, the exceedingly powerful lobby and advocacy group for older Americans.

And AARP is not happy with what it has heard from its members: complaints about incomprehensible service contracts, confusing bills and dead zones that are not clearly marked on coverage maps. They are the same concerns that have been expressed for years by other consumer advocates, who now have a new champion in the 35-million-member AARP.

We're hoping "to make the industry stand up and say, 'We've got to fix what's going on here,'" said Susan Weinstock, national coordinator, economic and utility issues, with AARP.

The group has already prompted the introduction of legislation in New York state that would provide more flexibility in canceling cell phone contracts, and it plans similar efforts in other states. AARP's campaign, which includes lobbying Congress, the Federal Communications Commission and state legislatures, and talk of running its own cell phone service, has caught the cell phone industry off guard. Consumer advocates say AARP's aggressiveness also reflects its own internal dynamics, and that AARP is focusing on such a universally and easily agreed upon position to unite a membership angered and torn by the turmoil of last year's divisive Medicare fight.

The cell phone industry has argued that it has done a good job of serving the needs of older customers and that what is best for people on fixed incomes is an industry free from taxation and regulation and thus, theoretically, able to offer lower prices.

Late in September, the two groups met for the first time to discuss common ground and their differences.

While about 80 percent of people 19 to 65 own mobile phones and more than 45 percent of those 10 to 18 do, only 39 percent of people 65 and older use them, according to the Yankee Group, a research firm.

Moreover, older people who do use phones spend considerably less money for fewer minutes each month than do Americans under the age of 65, according to the firm.