The standby option of the Nortel solution requires 3 re-boots of the "standby" server. It also requires reconfiguration of the Standby Servers IP address/hostname to be that of what was the Active Server. So that when ever one wants to go to the standby server, it requires an operator to be at the windows console to do this re-configuration, re-booting etc etc to make it happen. And this is all on top of the estimated 15 minutes for the replication from the active SCCS database to replicate to the Standby SCCS database.
As for Symposium doing CTI, Symposium call center server (SCCS) is not a CTI platform. To do CTI, one needs the Symposium TAPI Server which relies of the native support provided by the Windows OS for TAPI.