The rumors were true
Thanks to JerseyDevil for breaking the story while I was asleep having nightmares about ostriches looking in my windows.
The deal is structured as a tax free exchange called a Reverse Morris Trust. CBS shareholders will own about 3/4th of the combined company. Current CBS shareholders (which will still own the TV network) will have the option of selling the Entercom stock if they are willing to pay taxes on the gain.
Here is a longer term prediction. Some or all of Cumulus wil be merged into EntercomCBS. The FCC is very receptive to eliminating the ownership caps, which might allow Entercom to own more stations than they could today.