For those operators planning to deploy WiMAX systems in the unlicensed bands (currently 5.8 GHz only for WiMAX) there are no existing owners of the bands.  They may be freely deployed by anyone wishing to use the spectrum.  Providers merely need to buy equipment compliant to the FCC rules pertaining to the particular spectrum in question then deploy and operate the gear in accordance with the rules set for the specific band. 

The most usable and untapped spectrum range for multipoint service in the US is in the 2.5 GHz range.  The far majority of that spectrum is controlled by two companies Sprint/Nextel and Clearwire which are set to merge their 2.5 GHz assets in 2008, with about another fifteen percent being owned or controlled by multiple entities.  The second most commonly deployed and usable spectrum is at 2.3 GHz which is seeing some steady WiMAX deployments already.  The new AWS spectrum ranges at 1.7 GHz and 2.1 GHz will soon be major players in the US marketplace but likely not for WiMAX radios.  One potential band of great interest is at 700 MHz, which could see a WiMAX product in the near future. 

Regarding ownership, the BRS bands in 2.5 GHz are purely commercial and were originally intended for wireless cable TV.  In recent years the FCC repositioned the frequencies somewhat (redefining channel sizes for example) and began permitting mobile service in this spectrum range.  There is an additional and larger block of frequencies in the same spectrum range called EBS held mostly by school systems, universities and religious organizations.  These bands were intended to deliver educational programming and cannot be owned for commercial purposes.  They can however be leased for commercial purposes if some educational elements are also fielded.  Some major holders of such spectrum in the US are the Catholic Church, a Hispanic Telecommunications group and other institutions of higher learning.