On item #1, digital refers to the internal exchange phone system in the building. For example, in the McKinney office, we have a digital phone system. This allows for features to be available on the office phone stations that wouldn't be possible with an analog system. On a digital phone system, you still have to dial out to reach another party. The phone system you're thinking about is an ISDN line which is always connected and you never have to dial. Not the same.
Unfortunately the current that flows through a building's digital phone system is destructive to analog devices, such as modems and fax machines. That's why you need an analog phone line brought into an office to handle most fax machine's communication. The same applies to the AV-OS unit. There are adapters available that can allow an analog device to interface to a digital phone system, but they usually have to be tuned for each building's digital phone system. One manufacturer's digital phone system is not the same as the next. Some digital phone systems don't even allow these adapters to automatically dial a number through the adapter. They might require one of the system's stations to be connected to the adapter and the number has to be manually dialed to make the connection. It's all dependent on the digital phone system's requirements. Nothing's standard.
Fortunately, analog telephone lines are standard, which is how our AV-OS can be plugged into any analog line and work.