Complex sentence: Entercom's WLKK was not be able to assume the WBEN-FM call letters, since the company had previously released the WBEN-FM call-letters for use on a Greater Media station in the Philadelphia area.
Split into simpler sentences: Entercom's WLKK was not able to assume the WBEN-FM call letters, since the company had previously released the WBEN-FM call-letters. They are in use on a Greater Media station in the Philadelphia area.