I had an idea for a smartphone "scanner" last year where I'd take the bare RTL board (from inside an RTL USB device) and then mount that inside an external battery case for a smartphone (not every model has external battery cases available so I'd have to pick one of them to be a prototype) along with a telescopic whip antenna inside the housing as well. When attached to the smartphone it would use the microUSB connector to power the device and make use of it - obviously the prototype smartphone choice would have to be something that supports OTG aka On-The-Go functionality for USB devices and provide power as well.
Then all that would be needed would be some nice application to make use of it as a "smart scanner" basically but two problems: 1) I haven't had the opportunity to put this kind of experimentation into action and 2) I'm not a programmer or software developer at all to any degree whatsoever so that's a dead stop for me unfortunately.
But I think the possibility does exist to create such a device and I believe it could be pretty damned awesome overall if I could actually construct it. Could make use of something like SDR Touch on Android but go much further than the (still) limited functionality that application offers.
Just something to dream about I suppose.