A lot depends on the trunks and the type of system they're connected to.
In general, a PRI trunk or a E&M trunk on a T1, the ring back tone in provided by what ever device it's connected to.
So if you're calling an IVR system and that system is connected to an E&M trunk, they're typically isn't ring back although I would think ring back could be added.
Now on a Mitel, I can't think of any way to stop ring back. I'll let others jump in here and correct my assumptions but I can't think of a situation where there wouldn't be ringback unless you are connected to a 3rd party device.
Ralph