If the attorney actively uses/receives faxes, then I would say yes, you should generally include it, unless your client specifies the contact information that he/she would like to make available to the public.
- If the attorney may receive faxes from non-clients or prospective clients, then this information would need to be included on the website to allow for this.
- If clients or other contacts will fax important forms, papers, etc. to the attorney, they might have lost a business card or a scrap of paper with the contact information and would expect to be able to find it on the website. Leaving out this information would not satisfy the user's needs and causes more difficulty for them to find the fax number.
However, your client may decide to leave out the fax number if they do not want the general public to be able to fax them. Some websites will only provide a contact form to reduce spam and protect their information.