Can you provide any further information?
For example, does IVM's status/log window indicate it sees an incoming call? If so, what does IVM report?
Is IVM set to 'On' mode? (top-left toolbar area)?
What happens when you perform a simulation call?
Edit: I saw your post in the other topic. I don't know what to suggest. I know that Vista causes lots of incompatibility problems for voice modems, and it seems to me that it mostly concerns Zoom cards. Is reverting to XP an option? Also, I'm pretty sure Zoom is the one to contact, I think their driver for Vista must be a bit buggy.