Seems like it should be part of the Win911 standby mode or an option at least. Both our Win911 servers try to answer the phone.
The V7 Win911 had a number of rings setting that could be used but that could leave you with the primary trying to answer when it should be in standby.
We added a feature where you can set a delay when using two WIN-911 systems on the same phone line. The Primary wll anwer first, and if not available, the Seconday will answer.