HTTPS Fax Adapters- These have flaws like delays, and it will tell you a fax went through when it really didn’t. Both of these things make these adapters unreliable. I’ve still got about 20 or so out there that I will be moving to T38.
G711 will Fail with something as little as a 2% packet loss or any amount of real Jitter. I definitely don’t recommend even trying this. I have more details on G711/Modem stuff but I won’t bore you.
T38 works extremely well if setup properly, and if you can step the fax machine down to 14400, after months, years of perfecting T38. I’ve finally make a new breakthrough tonight actually and I’ve got it working really reliably with 4 different carriers. Ran about 100 test faxes through today to different numbers. I even combined this new breakthrough with the FreePBX Trunk Balancing Module. So now instead of it going through the same carrier every time, I can have the trunks round robin. So when the fax machine sends it’s retries…it will try to go out several different carriers in case one has a bad route. When you try the same route over and over again and expect a different result…LOL. Some Fax machines allow you to set retries to 14 times. If you don’t want to mess with adjusting the fax baud rate to 14400, you can use a T38 Relay like audiocodes which will step the speed down for you before sending to freepbx.
Online only HIPPA Compliant Fax Providers. Like the FaxAge and SRFax. Great if they work reliably. Pricing is much better than someone like E-Fax. Still expensive though.
Copper Lines/ISP lines…Someone else’s problem and $30-$50 for unlimited calling.