I am not so sure about this "Device Selector" idea. And even if it was true that choosing a mobile device is hard, adding this to the equation might help some but most people don't like questionnaires and they tend to avoid answering questions on paper (or electronically) just to buy a phone (even if it was just an option).
Personally speaking, I think the salesman just needs to ask "selected' questions verbally to the customer and that should narrow the device selection down. And there will always be cases where the customer will buy a device and ends up back to your store to return it. This is common and happens to all kinds of products in general.
I don't know about you guys, but I don't like surveys and questionnaires. And if I had the time and patience to complete one, it has to be at most 10 simple questions. And to use such a method just for buying a phone sounds a bit out of context. Might work for others though.
Nevertheless, people will keep going through numerous mobile devices through-out their lives because new devices with better features and faster processors will always come out and make people buy them.