Ipkall is a DID only provider, and those are configured to point to your Voxalot account, not the way around.
Log in to Ipkall and fill the proper fields:
Code:
SIP Phone Number: XXXXXX (Where XXXXXX is your 6 digit Voxalot number.)
SIP Proxy: voxalot.com (or .com.au)
Then wait for an hour for changes to take effect.