If I could just... say this... um...
First of all, for the first idea, wouldn't it be better to just create a smartphone/iPhone app which has buttons with common phrases for the aforementioned situation? Obviously I think it's easy/fast enough to communicate through writing 9___9'' But if you really want the option of "speaking" to hearing people who don't know sign, then create a stinking app like that v___v''
And second of all, for the tool to help people learn ASL... I think it would be better described as a tool to help people REVIEW ASL. Like once they've already learned some signs they can practice and see if they're getting the message across that they intended... but for that, with the 5 parameters (as Jazzberry noted) being so complex, simply monitoring hand movements would not work. What would be better is if it was some sort of video tool which recorded data on ALL 5 parameters, watching for facial expression, eyebrows, head tilt and other body language etc. So as to differentiate between similar signs like "innocent" and "naive." But as technology is right now, that would be difficult to accomplish, as you'd need a pretty high-quality camera and some pretty nifty software. Long story short? Too flipping much of a cost and a hassle. Just go see a dang tutor or video chat online if you want to make sure you're signing right.
Sorry if that sounded harsh, but I'm just sayin'.