I just went to Sprint and started the order process on an overdrive pro and it still shows 4G as unlimited. The 3G is limited.
The only unlimited data that sprint took away was the hotspot on phone feature which they now limit to 5GB. Bad move on their part, especially not grandfathering people in, but unless I'm missing something 4g is still unlimited for data cards.
As to the original question, you'd have to get a clearwire modem or hotspot.