these days almose everybody ll came online at least once in a day from mobile, intensionally or absend mindly, and for us its important to know from where they are online, for eg. if they are on travel, it may be trouble for them to accept a chat
here is a Gmail Lab feature to identify Android Chatters from the list
for this go to gmail lab from the top lab icon and enable Greenrobot
Chat buddies show up as robot icons if they are currently using Android. Helpful to determine if you are chatting with someone on a computer or someone on an Android device.