A powerful new alliance of giant communications companies is taking shape just in time to bid for new slices of the airwaves under SprintŐs national brand umbrella. The nationŐs No. 3 long-distance phone company announced today it would team with three leading cable TV operators -- TCI, Comcast, and Cox -- to compete with Baby Bells and establish a national wireless communication network. Dealmaking in the wireless business has accelerated in the past month. Also in just ahead of the FCC's Friday deadline: Bell Atlantic-Nynex and U S West-AirTouch.