A mate and I have completed extensive testing of the IVM and also Axon, Express Talk and IMS.
With regards to IVM, we can get this working fine with the Australian VoIP provider Engin - however, Engin's call quality is not very good and they do not support multiple incoming calls (which is our requirement) on the one phone number.
On the other hand, ISPhone.com.au has exceptional quality (the only VoIP provider I would consider using in Australia because they have high quality audio ie. they do not limit the quality to save on bandwidth) and they do not route their calls via international links - all of which means much better quality when compared with the likes of Engin.
The issue with IVM and ISPhone
The IVM does not work when calling an ISPhone VoIP number from a POTS phone number (or mobile phone). The caller can not hear the IVM!!! (However, it works if you call the ISPhone VoIP number from ISPhone VoIP line.) This also happens using Express Talk, however (and this is the weird part), if you click "Hold", then the caller can hear the hold music and then when the call comes off Hold, the caller can then hear the person on the other end.
Please note: That the Express Phone works when used with Asterisk and ISPhone. Therefore, the issue is either in the IVM software (when using just the IVM by itself) or with Axon (when testing the Express Phone).
With the IVM and ISPhone it is an almost perfect solution, so it is a real shame that this does not work.
Is there any way to make the caller, when they call, automatically be put on hold and then taken off hold to listen to the IVM?
Does anyone have the IVM working with ISPhone?