The default settings in the OBi should handle most situations.
If you're on an incoming call and you get another incoming call, a normal hook flash should switch calls. The exception would be if you're on a PSTN call and get a call waiting indication from your PSTN provider. In this case, your would need to use a double hook flash:
A double hook flash event is two successive hook flash events that are less than 700ms apart (by default). If this event is enabled, the device will generate a hook flash signal on the PSTN line if the phone is currently on a call on the line. This option is useful only if HookFlashHandling is set to "Handle Hook Flash Locally".
