We have setup exchange 2010 voicemail which works fine from internal. ie, we dial the voicemail extension which is redirected to exchange and all audio prompts from exchange are heard and email sent.
However if its from an external caller it is redirected to the exchange voicemail but cannot hear any audio from it. We receive email stating that there was a call.

I have tried looking at the IP routing as it is on a separate VLAN.

Would appreciate some guidance on this one.

Regards Nick.