The first smartphone, I'd say, should be defined as the first device that was attributed to be a smartphone (either coined the term or was introduced as a smartphone) and as would have been available for purchase by the mass market (even if it was expensive). I think it could be argued that the first designed or prototyped smartphone should be considered and thought about, but I think a product that actually made it to market is more worthy of that title.

I've been looking around a bit and the most prominent out there is Simon (http://www.businessweek.com/articles/2012-06-29/before-iphone-and-android-came-simon-the-first-smartphone) but not sure if that's exactly the case.

Would love to hear everyone's thoughts!