In order to add these Yahoo! Messenger status button to your Blogger blog. Go to dashboard of your blog, click on Layout tab and then click on add a gadget button and select HTML/JavaScript as instructed in the image below.
copy the code below and paste it and don't forget to change YOUR-YAHOO-MESSENGER-ID to your actual Yahoo! id as mentioned above.
please be aware, there are 2(two) YOUR-YAHOO-MESSENGER-ID in the code and you have to change both of them with your actual Yahoo! id.
Good luck !!