The IEEE has started work on a 1Gbit/s version of WiMax which could seize the coveted "4G" prize, and replace both cellular and WiMax.
The IEEE says it will have the 802.16m standard ready during 2009, and it will use current OFDM and MIMO technologies, with which companies including NTT DoCoMo have already demonstrated Gigabit wireless speeds. It will also have backwards compatibility with the current mobile WiMax standard, 802.16e, and will also be suitable for fixed as well as mobile links.
To get to this Nirvana, there are technology issues, like packing the multiple antennas which the technology requires (NTT DoCoMo used four) into a mobile device -- although work is underway to minimize multiple antennas onto PCBs that can be placed inside portable devices.
The larger problem will be the political one: if this standard is to converge the two worlds of 3G and WiMax, then an IEEE standard must be accepted as the next step in the cellular road map, which is determined by the ITU telecom standards body, with the operator-led 3GPP group. Although US operator Sprint has adopted WiMax, most operators have been hostile.