In Organisations with multiple groups, the groups can be set to inherit a common address book (Contact List).
This means all users in the organisation see the same contact list, regardless of which project or group they belong to.
The setting can be controlled with a checkbox in General Settings area of each group.
To do this,
1) Click on Contacts
2) Select the Import Symbol
3) Choose File to import your Excel Spreadsheet of your contact list.