Plugin author Chad Y. has created a cool little tool for Gmail. It allows you to see which of your friends are currently using their Android device. This is helpful to know when someone might be chatting from their phone instead of a keyboard. Just login to Gmail and enable the feature under Labs.
A similar feature is also available with the desktop version of Google Talk. Each contact that is signed into their phone will display a little icon next to their avatar. The desktop Google Talk icon isn’t for someone logged in from their phone — it’s indicating someone using their talk account on a VOIP capable device (Thanks Lemon).
And finally (for those who were wondering) an Android status icon is included in the native Google Talk client for Android as well.