the most interesting line in that whole article is that WEEI wants to keep him because he voices spots for a sponsor.
Now, not being a listener I have no idea who he is hawking, but it must be a major advertiser that Entercom is afraid will walk, or want to renegotiate the contract if Callahan is not the guy voicing their spots.
I have been told that one of the reasons one of the WMJX air staff is secure in their position is that a major advertiser won't buy unless it is a certain talent in a certain daypart.
It seems to me that the only leverage one has with their employers in this business is the relationship with a major client.