The app will let you chat with individuals as well as groups. It will use push notifications to let you know when a message comes in. You'll also get a unique seven-digit PIN for Hello, which the app's creators say will help you protect your privacy while making it easy to chat with friends without racking up SMS fees.

Andrew Hanhauser of Hello told me via e-mail that the app was submitted to Apple for approval this week, which could mean that it arrives on the App Store as soon as the beginning March. An Android version is also in the works; that's slated to be completed in another month or two.

San Francisco is turning out to be the proving ground for an app that lets would-be taxi passengers hail a cab with a simple tap. is a free app for the iPhone that shows you a map of nearby cabs that you can hail simply by tapping their icon. In addition to one-touch hailing, the latest version of Cabulous--which was on display at Expo--also lets you send a note to the driver containing information such as where you want to go or where you want to be picked up. Passengers can also tag drivers as favorites, making it easier to give them repeat business.

Of course, for such a service to work, drivers will have to use Cabulous, too. To that end, developer says its signed up more than 150 cabs in the San Francisco Bay Area since launching the app at the beginning of January. The UpStart Mobile rep at Expo told me the service had just passed the 2,000-fare mark last week.