Update a single contact for multiple mailboxes

Hi,

We are using Exchange server 2007 SP3

We have pushed an outlook contact containing Helpdesk contact information to all users mailboxes using Import-mailbox commandlet. We used command as belw

Import-CSV -path users.csv | forEach-Object -process { Import-Mailbox -Identity $_.UserName -PSTFolderPath C:\contacts.pst -IncludeFolders '\contacts'}

Now we want to update some information(e.g. telephone number) within this same contact object for all users?

We tried using Import-mailbox again but the information within contact object does not change. How can we achieve this?

please help.