The rumor mill suggests that Sprint might be collaborating with Walmart to expand its WiMax network. The carrier plans to launch WiMax-ready handsets later this year, but coverage is still lacking. This could be remedied of course, if Sprint follows through on its reported interest of placing WiMax cells on top of every Walmart store.
An anonymous source cited by AndroidGuys claims they have been asked to determine how many stores overlap each other in a 30 to 50 mile radius. It was concluded that the plan would provide sufficient coverage for a large portion of the US, and it would cost less than erecting towers and dealing with hassles and zoning permissions.
Despite its colossal count of retail locations, I imagine affixing WiMax towers on every Walmart store would still leave plenty of gaps in coverage.