Sprint's 4G WiMAX network has been clearly a technological dead end for a while. But in researching 'The Mobile Internet Handbook', I was able to dig up when that dead end turns into a brick wall.
Sprint is currently planning to shut down it's WiMAX network entirely by the end of 2015, freeing up spectrum to use for the Sprint "Spark" extended LTE service.
If you currently use a WiMAX compatible device, be prepared to be orphaned at some point next year as Sprint prepares to shut down various areas.
And be very careful to avoid signing up for any MVNO's that use Sprint's WiMAX network. You may get a bargain now (and perhaps even unlimited data!), but the service you are buying will not be around for long.
If you do happen to be in a WiMAX served area and are craving fast unlimited data, the H2O Wireless Bolt plan will do the job for just $50/mo.
Just don't get to attached to it...