Voice Mail Setup

I am using VoipDiscount and IPKall. Initially I set up IPKall to forward call to VD; no problem and able to receive call.

But when I set up voicemail using Voxalot,and have IPKall forward to Voxalot, then call always forward to voicemail.

In Voxalot, I set up the voice service provider like this:
Username: my VD username
password: my VD pw
Host: sip.voipdiscount.com
SIP Register: No (because I am using basic FREE service)

Any help??