People keeps on pinging me when I'm online on mobile and its been difficult for me to reply to them with my clumsy touch keypad. So enable this from the GMail labs and get know whether if your friends is online on a PC or on his Android.
To activate this go to https://mail.google.com/mail/u/0/#settings/labs
and in the search box type "green robot".
Enable the "Green Robot" feature and you can find if you friends are on their Android.
If your friend is online on his Android device online status of his is shown by a Green Robot Symbol.
