Each quarter Level 3 Communications has been making progress in growing its Core Network Services (CNS) revenues, with enterprise services being the key driver. This trend continued into the fourth quarter of 2014, where CNS and enterprise revenues rose to $1.46 billion and $1.01 billion, respectively. And while AT&T (NYSE: T) and Verizon (NYSE: VZ) are still two of the largest enterprise service providers, Level 3 could become an even bigger threat to these carriers. In his latest column, FierceTelecom outlines five good reasons why AT&T and Verizon should worry about Level 3. You can read it here.