KSL can refuse to air commercial time to the Knights of the Ku Klux Klan, the American Communist Party, or Girls Gone Wild. (Watch what's on network TV at 3:00am. It's advertisements for financial planners, exercise videos, non-stick frying pans, and skincare products.)
Reagan Billboards has a right not to advertise something they find objectionable... According to your theory, a competitor could force Reagan to put up a billboard that says "Reagan Billboards suck! They are thieves and idiots. Use Company X!"
...because of free speech.
Also, in a phone call, you're calling one person.
A media company is essentially giving people a megaphone