The difference in the phone does not matter. The Everything/Unlimited Plan does not include tethering. Sprint has put a block on this option being used for free on its phones now via the network. There is no way to use the phone as a modem without buying a tethering package or Tether (tetherberry).
Posted from my CrackBerry at wapforums.crackberry.com
I can confirm as I just changed from the simply everything plan to a normal plan + data + tethering and it works great. I am seeing about 1000K+ DL speeds. The tethering plan is $15 extra per month. Tether formerly tetherberry is also a great product.