The NetVanta 7100 only has one System Mode for the whole system. The addition of a BCS system can accomplish multiple system modes for a tenant system but the modes can only be set via an auto attendant and not from a line key on a phone. The modes are set by changing a value in a database which the BCS checks each time a call comes in. That is why the line keys don't work. Can't program a DB check to a line key.
Sorry that the standalone system won't meet your application. Let me know if you have any other questions.
Thanks. I ended up showing the customer how to change the greeting from the web application. They are happy!