Imus does have a right to free speech--in his own living room, on his ranch, on a public street corner, in the halls of Congress or in any other public forum.
However, CBS, MSNBC and Infinity Broadcasting do have every right to dictate what he can and can't say while he's sitting behind a microphone that they own
Letting two race hustlers like Sharpton and Jackson call the tune is disgraceful, but again, the folks who own the radio stations can dance to whatever tune they want.
Imus has the cash to buy his own station, if he wants to. He has a broadcast studio at his ranch. He can buy the equipment to air his own show and if he can find enough advertisers, and enough stations willing to syndicate it, he can say whatever the hell he wants
Imus isn't the first guy in NYC to get in hot water by saying something stupid. Bob Grant was fired by WABC after publicly celebrating the death of Clinton's Commerce Secretary, Ron Brown, in a plane crash. He moved right over to another station and kept on saying the same things.