as far as adding it in the same place where those other icons are listed, SMF For Free is the only one that can add those. You only have the ability (at the moment) to change those current icons to something different by using the image swapper. However, you can add something similar yourself by using this:

http://www.smfsupport.com/support/guides_and_tutorials/guide_custom_profile_fields_all_smf_versions-t3061.0.html;msg17314#msg17314

You can use it to create a place for people to input a screenname, etc. You can set it up to where it only shows on the members profile OR you can have it show up in their posts.