When the term WiMAX 2 is used, it's actually referring to WiMAX Release 2. Currently, WiMAX uses the IEEE 802.16e revision, whereas the 802.11m standard has been submitted for IMT-Advanced standardization to the ITU.
WiMAX Revision 2 is expected to begin use commercially around the world between the years 2011 and 2012.
Amongst other things, 802.11m will boost data speeds up to four times compared to current generation WiMAX systems. WiMAX Release 2 provides for strong backwards compatibility with WiMAX Release 1.
Network operators will be able to upgrade to WiMAX Release 2 relatively easily, usually requiring upgrading channel cards or software on their systems. Users of current WiMAX products will be able to utilize WiMAX Revision 2 networks without a problem.
