So, what is the killer application for mobile WiMax? Come on, you knew this question was coming at some point.

Actually, I was chatting to a few people about this at the Light Reading Live backhaul event in Atlanta last week. (See Stitching the Backhaul Quilt.) Its an issue that's starting to come to the fore as mobile WiMax networks are being installed now in the U.S. and elsewhere.

As you might expect, no one I spoke to is really quite sure yet what the application will be that drives people to use WiMax. There are plenty of options, however.

Obviously, streaming video and mobile TV are being considered as popular choices. We could even see dedicated devices for mobile viewing applications.

Voice-over-WiMax is definitely an option. It'll be interesting to see how service providers think about pricing VOIP, particularly as they will be competing with Skype Ltd. or similar free services.

Personally, for me as a consumer, I think that wireless MP3 downloads over WiMax could be something that encourages me to move to this new network technology. The engineers I spoke to at the show suggest that such a service could be difficult to manage because of the bandwidth requirements.

Of course, for Sprint Corp. (NYSE: S) the correct answer to the killer app question might be "all of them." Certainly, Chief Technology Officer and President of 4G Mobile Broadband Barry West talked about a lot of different applications at CTIA recently. (See CTIA: West Talks WiMax.)Interestingly, what people actually want may be simpler than lots of new applications. Respondents to our mobile WiMax poll voted for "faster downloads" as their key application rather than anything fancy like video or music. (See Mobile WiMax.)

— Dan Jones, Site Editor, Unstrung