A site administrator can put on an additional line for contact information.
Adding an additional contact setting
Click on Admin.
Choose Contact settings. Another window will open that will enable you to put an additional field to key in information such as another mobile number, or landline, or extension.
Fill out the mandatory fields 'Name' and 'Apply to' then save. You will see the new contact field added depending on where you choose to apply it (user profile, roster, location, and/or phone book profile).