I was asked to look for an online fax solution. A provider I contacted never called me back. Do you offer subscriptions even if they are not needed? I know next to nothing about faxing - how is the transmitted data secured? Is it?
Out of curiosity what’s your use case? There are lots of subscription fax services out there (efax and hellofax are 2 popular ones)
Other than that you can do things in-house with Hylafax and either hardware (e.g. Mainpine boards, expensive but they Just Work) or software solutions. My experience with software solutions (IAXModem with Hylafax and Asterisk) has been that speeds and reliability are sometimes poor, at least compared to good hardware solutions or physical fax machines supporting 33.6k.
And 9600 is usually required to get faxes through to a lot of places, because everyone is trying to do fax over VoIP, and that is generally tough sledding, if it's possible at all.
Traditionally, transmitting a fax was just making a telephone call so it was vulnerable in the same way that any telephone call was to wiretapping. With fax services as exist today, you're basically emailing them a PDF and they're then sending that as a fax to someone's phone number. (Or the reverse.) So there's no real security other than that provided by the telephone network and the service's internal controls.
I had efax for a number of years but I believe they eliminated the free incoming fax number for free accounts and I haven't actually needed to send or receive an actual fax (as opposed to a scanned document) in years.