After years of impunity, America’s 190 million cellular telephone subscribers are now more apt than ever to encounter telemarketers. There was a rash of complaints to federal regulators 18 months ago when telemarketers were confused by new rules allowing people to transfer their home telephone numbers to cell phones, which then started ringing with telemarketing calls. Then in March, BellCanada cellular customers were targeted by a company pitching a low-cost trip to Mexico. The same message has recently surfaced in San Francisco.Just about the only recourse a consumer has is to subscribe to the National Do Not Call Registry.