Research in Motion has added the ability for BlackBerry users to install apps on their phone by visiting a web site in a desktop browser. The feature is part of the updated BlackBerry App World store for mobile apps.
The push to service requires a browser plugin which only works on Windows right now, so Mac and Linux can’t play. During the setup process you’ll have to sign in with your BlackBerry ID and connect your phone to your PC using a USB connection. Once you’ve done that, you’ll be able to push a download button on the web site to automatically download apps to your phone, whether it’s plugged in or not.
Google is expected to launch a similar service for Android phones, but right now the closest thing I can think of is the third party AppBrain market for Android phones which lets you install and uninstall apps from the web by running an AppBrain client on your mobile phone.