While fax is not officially supported, there is a section with several tips in the Ooma Support Knowledgebase, which I highlighted below. Short version: Connect your fax machine directly to the Hub, and dial *99 before your fax number. Both sending and receiving worked perfectly for me on the first try. I’m very impressed!
While the ooma system is not guaranteed for Fax transmissions, it often works successfully, provided you follow these simple instructions:
1. For the best results, make sure your Fax machine is connected to the back of the ooma Hub or Telo unit, not the ooma Scout. The fax machine should be plugged into the “PHONE” port of the ooma device. If you plan on using a phone handset with the ooma Hub or Telo, you can use a splitter to connect a phone handset and the fax machine to the ooma device.
2. Dial the prefix *99 before you dial an outgoing Fax call. Please note that you may need to insert a pause or two in the dialing sequence after entering the *99 prefix and before entering the Fax number.
If you are still unable to send or receive a Fax, try the following additional steps:
1. Disable “ECM” (i.e., “Error Correction Mode”) on your Fax machine.
2. Decrease the transmission or baud rate.
3. Reduce the number of pages that are sent per fax.
4. Decrease the desired image quality of the fax.
5. Discontinue any large file downloads (for receiving faxes) or uploads (for sending faxes).