I think executionally it's a great idea. The thing is - telephones were always used as an input channel because people were listening to the radio and NOT doing something else. Maybe there's a live tv application here - maybe event programming makes sense (you could sell this off to a progressive experiential marketing agency - Jack Morton/etc.) for promotional elements.
The long and short of it is - think of the required use/application and where this actually fits. Or if not, create a use for it and monetize.
I think that paraschopra is right in the determining whether there is an existing need for this. Though, my approach is - what's the application that this could be really great for? Whether it exists, or is exactly on-site billing at a client -I think the answer is - where is this a killer app? Isn't there a great application for pop-up sales events? Fairs, trade shows, etc?