Online presence allows people to see if you are currently online and using Yahoo! Messenger. To add online presence, you simply need to add some HTML to your web page.
If a Yahoo! Messenger user clicks your online presence, an instant message window will open for them so they can type you an instant message.
Prepare this code:
<img border=0 src="http://opi.yahoo.com/online?u=
Please notice for bold text above. Then change to yours.
For t=1, you can change the value according these pictures:
To see the result, just take a look at right of this page. 😉