Here's the website for the service I first heard about at Sun N Fun. I've
signed up and it seems to work perfectly.

I have the Samsung i700 which has a cellular modem (and unlimited internet
access through Verizon). I've found http://www.accuweather.com/pda to be a
good, free weather site. DUATS works well with it too.

I assume it's not legal for use in flight though, and I don't see how this
service is any different - is it?