I also work at a startup in the location space. If you're just looking to play around and have fun, I'd definitely recommend avoiding the "feature phones" (J2ME

I also work at a startup in the location space. If you're just looking to play around and have fun, I'd definitely recommend avoiding the "feature phones" (J2ME and BREW) and focusing instead in Symbian and Blackberry. Most Windows Mobile devices in the US don't allow access to GPS or have it deliberatly crippled (The Sprint Mogul and AT&T Tilt are the only two I know of with user accessible GPS). iPhone is still an unknown, as I doubt Apple will open up its app store to every developer and every app. Right now it's probably best to wait and see. Android is, well, not out yet. Wait for a device to make it to market. WHERE is also a fast easy way to get one shot fixes and rapidly deploy an application to the millions of "feature phones" out there already, but it won't give you background updates or complete control over the user experience.