The two WiMAX providers are banking on licensing wireless frequencies used by educational, government and non-profit organizations to fill out their coverage but have only brought their use of their private, already-used commercial frequencies to regulators, according to AT&T. This approach has allegedly let both Clearwire and Sprint grab a large amount of spectrum for a wide-area Internet service without having to undergo the same vetting process as rivals.

Sprint itself has said the use non-commercial spectrum has received explicit support from those that manage it, as the organizations will be allowed to use the fast mobile data for their own purposes and earn money by leasing the spectrum to the carriers using it for their own services.

AT&T has a potential motivation to slow the unveiling of the joint WiMAX project, which is officially due for a few cities in September. WiMAX is considered a fourth-generation (4G) mobile Internet technology and will compete directly with AT&T's planned Long Term Evolution network, which was the result of successful bidding in the FCC's recent 700MHz wireless auction and will also offer 4G-class speeds across the US.

The mutual Clearwire and Sprint project will also allow any device and legal software program to join the service, opening the possibility of hybrid devices switching from AT&T to WiMAX.