Deligate user to update their self information on AD such as phone number.

Best Practices for Delegating Active Directory Administration
http://www.microsoft.com/downloads/details.aspx?familyid=631747a3-79e1-48fa-9730-dae7c0a1d6d3&displaylang=en

In the appendice of this document, you'll find the exact rights necessary. I suppose the right should be given to 'SELF'

Thanks, but I hope to know step by step procedure with some example.

on the GPO containing the users, right click on it, and select properties.
Go into security, advanced
Click Add...
type SELF, and click OK
(optional: if users name or account contain 'self', they will show here, so select the one with 'SELF' as RDN, and click OK)
in PERMISSIONS ENTRY FOR USERS: on the Properties Tab,
in Apply onto, select User Objects,
then select the permission/proipery you want to apply.
Once finished, click OK as menay times as necessary to close the windows...

exemple of permissions you'll find:
'Write General Information', will allow the user to edit his email and phone number...

though I can see there is a specific one for mail and phone too: 'Write Phone and Mail Option'...

Thanks! Very helpful.