This would be a pretty amazing application to have - esp on a phone.

Quoted: What if you could look at your cell phone and see a heat map of where everybody in the city was at that ...

Google Code home page for Android (GPhone) development (including information on the $10M development challenge Google is offering to kick-start Android development).

Quoted: Welcome to the Open Handset Alliance™, a group of more than 30 technology and mobile companies who have come together to accelerate innovation in mobile and offer consumers a richer, less expensive, and better mobile experience. Together we have developed Android™, the first complete, open, and free mobile platform.

The Android/Google Phone browser is based on WebKit.

Quoted: WebKit is an open source web browser engine. WebKit is also the name of the Mac OS X system framework version of the engine that's used by Safari, Dashboard, Mail, and many other OS X applications. WebKit's HTML and JavaScript code began as a branch of the KHTML and KJS libraries from KDE. This website is also the home of S60's S60 WebKit development.

Excellent article about Andy Rubin who developed the SideKick phone, and is now directing Google's efforts to develop a mobile phone.

Quoted: With battle lines being drawn in the smartphone market, Google is placing its bets in the hands of Andy Rubin.

John Manning's company. I've not see the site in a while - the design is really good.

Quoted: Make custom ringtones and wallpaper for your cell phone. Convert any music or picture file. Free ringtone trial offer. 100's of phones supported.

Satoshi's mobile application platform company - now a subsidiary of Square Enix.

Quoted: “When founding UIEvolution, my goal was to develop software that delivers a rich, interactive mobile and broadband content experience to millions of users worldwide.”
-Satoshi Nakajima, Founder and CEO of UIEvolution

Twitter helps you stay in touch with friends via SMS messaging. You friends can subscribe to receive SMS updates whenever you post. It's kind of like a personalized distribution list for SMS messaging.

I noticed that Scoble is using this extensively and has 100's of people following his posts.

Quote: Twitter is for staying in touch and keeping up with friends no matter where you are or what you’re doing. For some friends you might want instant mobile updates—for others, you can just check the web. Invite your friends to Twitter and decide how connected you want you to be.

New mobile application from Yahoo. Mentioned at the iPhone launch (though not shown on the iPhone!). Note that iPhone is still 6(!) months from being shipped.

I also couldn't download Yahoo! Go 2.0 for my BlackBerry as the beta was "full".

Quoted: Yahoo! Go. Put the power of the Internet in your pocket. Email, local info & maps, favorite news, sports teams, weather, Flickr photos, and search.