An hourly cell phone store worker half a world away from cupertino is not going to have that info. Only a handful of people at Apple HQ knew details about the iphone before it was introduced at MacWorld last year.
Nevertheless, an iphone nano will likely appear sooner than later. Just as Apple released the ipod shuffle to take a bite out of the low end mp3 market, an iphone nano priced at $99 will take a huge bite out of the entry level phone market. It'll be simple, with no touch screen and maybe no internet access, but will be very attractive to the low end phone set who just want a basic phone and music player in one package. I'd look for this to be announced, if not released, at wwdc with shipping definitely occurring before the 2008 holiday season.