While doing some research on which frequency bands mobile WiMAX will be specified for I found this interesting website from Intel in which they give some information about the upcoming Rosedale 2 chip. They say that Centrino notebooks with the chipset will support both Wifi and WiMAX.
Supported WiMAX Frequency Bands
A link to this .pdf document gives further info on the bands supported by the chip. Looks like it will cover the most important band for the U.S., which is 2.5 GHz and also the 3.5 GHz band which will be used in Europe and Latin America. Good preconditions for mobile roaming. I wonder which bands will be used in Asia!? Also, the pdf document gives a good introduction to the WiMAX network architecture and how Intel plans to integrate WiMAX into notebooks.
Multiple Wireless Technologies with one SIM card
Also, take a closer look at the figures at the end of the document. Looks like Intel would like to see interfaces for authentication and billing into 3GPP2 networks (i.e. current EVDO networks). This would make quite a lot of sense for carriers like Sprint who will deploy WiMAX networks along their already existing EVDO networks. Such an interface would be required for what Intel calls "smart card re-use […] for support of seamless authentication while roaming across technologies" which Intel says "is under investigation". The wording suggests that they are not sure about this detail yet.