If you need a faxing service that uses HIPAA standards and will give you a written statement to this effect, I suggest sfax from Scrypt:
Note: This link is an affiliate link.
I've had multiple problems with my landline in trying to send and receive faxes, and their services have solved this problem.
Also, you can use it from month-to-month to see if it will work for you or not. No contracts are required, and it comes with an 800 number.