Had an interesting chat with a company called Comsys this afternoon. It makes baseband chips for mobile phones. It's working hard on the notion of a different style of dual-mode that I hadn't really given much thought to up until now - combining wide-coverage GPRS/EDGE with more localised WiMAX for high capacity in urban areas.
I can sort of see the argument - especially for 2G operators & MVNOs that don't have existing UMTS spectrum or built-out networks, and think that 802.16e might be cheaper or easier to deploy. Conversely, it may be that such devices would enable WiMAX startup operators to start off with lower capex if they concentrated on build-out in dense areas, and cut an MVNO deal for occasional rural use.
One problem might be indoor coverage, however - I can't see 2.5GHz or 3.5GHz WiMAX having great penetration in-building, which may mean WiFi is needed as well. Another thorny question is around authentication - although Comsys is positioning WiMAX as "a cellular-type technology" I haven't seen much enthusiasm for using SIMs with it thus far, although I guess that a UMA or VCC approach might work.
Nevertheless, an interesting option & worth keeping an eye on.