1. Build it out - it's capitally intensive to build out a national network so a wireless carrier partner is necessary. Why a carrier? It's in their core competency to implement and run networks. Sprint is in the best position to meet DISH's wireless buildout goal with its Network Vision (spectrum hosting capability) strategy. Stating the obvious - having a carrier such as Sprint host allows DISH to bring services up quickly and minimize a huge self-built price tag.
BUT........
Don't forget the devices that will run on the DISH spectrum. Device and chip makers haven't exactly created product yet to meet this need. There is a ramp up time to incorporate it into the product portfolios. It doesn't happen overnight - look at the time in which Sprint/Clearwire announced TD-LTE 2.5 GHz support to when devices will have that band and technology incorporated. This is a factor in both the above scenarios.
Let's see what DISH does.........