How do I send a fax using OBiFAX. there doesn't seem to be a guide?
OBiEXTRAs's Fax-to-Email you mean?
Exactly that, Faxing to email. But you are trying to send out a fax with the OBiEXTRAs. OBiEXTRAs does not have "send out" capability, only incoming fax.
if you have only 1 phone port (OBi200 device) and with Google Voice service, unplug phone, plug the fax machine line to the phone port and go for incoming/outgoing faxes with someone that also has a fax machine to receive and faxing out to you.
If you have OBi202 device, designate another Google Voice account, isolate to Phone 2 Port mainly for your fax machine line for all fax in and out.
Good luck!