As demonstrated by high-profile deals with the National Football League and Cowboys Stadium over the past 60 days, few categories represent as much opportunity as wireless services.The primary reason: industry consolidation.Mergers and acquisitions have bolstered the sponsorship resolve at the four major U.S. players—AT&T Inc., Sprint Corp., T-Mobile USA, Inc. and Verizon Communications Inc.—all of which are increasingly using sponsorship to build consideration, preference, and u...