adx supports various online accounts for each contact. This will be shown mostly as bookmark link (e.g. to twitter) or as direct interaction link (e.g. for Skype).
addressbook.xml:
<contact>
<forename>Thomas</forename>
<surname>Bartensud</surname>
...
<account type="twitter">bartensud</account>
<account type="facebook">bartensud</account>
<account type="last.fm">Bartensud</account>
<account type="Skype">bartensud</account>
...
</contact>
Result:

<contact>
..
<account type="${type}">${userID}</account>
..
</contact>
Currently supported account types (case in-sensitive values for ${type}):
Value for ${userID} is basically an unique user id used at the specific account type. ${userID} is part of the URL which is built from for this account, e.g.
<account type="twitter">bartensud</account>
results in http://www.twitter.com/bartensud
There's also a generic way to link to arbitrary accouts:
${type}: arbitrary string which will be shown as link text (e.g. abcdef)${userID}: Complete URL to your account (e.g. http://abc-def.net/user/bartensud)<account type="abcdef">http://abc-def.net/user/bartensud</account><account type="bebo">${userID}</account>
will be resolved to your profile site at bebo.com
Possible values for userID:
<account type="ebay">${userID}</account>
will be resolved to your profile site at ebay.com
Possible values for userID:
<account type="facebook">${userID}</account>
will be resolved to your profile site at facebook.com
Possible values for userID:
<account type="flickr">${userID}</account>
will be resolved to your profile site at flickr.com
Possible values for userID:
<account type="Google">${userID}</account>
will be resolved to your profile site at Google: http://www.google.com/profiles/${userID}
It may be necessary to create your Google profile explicitly although you've already an account.
Values for userID:
<account type="studiVZ">${userID}</account>
will be resolved to your profile site at studiVZ: http://www.studivz.net/Profile/${userID}
Values for userID:
Example:
<account type="studiVZ">250c34b1fe2eafa2</account>