Also, you wouldn't be able to make international calls from the BYOD line.

While the BYOD line (primary number DID) can be operated in a different location from the VOIPo ATA, the add-on line(2nd number DID) must be in the same location as the VOIPo ATA. In other words, one location would have the VOIPo ATA running both your primary and add-on lines, and able to make international calls, while the other location would have a BYOD ATA running your primary line, and unable to make international calls.