Two months ago, the FCC set rules limiting how much spectrum Verizon and AT&T can buy through the auction. That opens the door for Sprint and T-Mobile to grab a large chunk of the airwaves. Each has a relative dearth of low-frequency spectrum (superior for rural and in-building coverage).
Sprint currently has $26.6B in net debt, and T-Mobile roughly $9B. Shares of both companies have fallen on the report.