My suggestion is to NOT register your Callcentric account to be able to make use of the Callcentric features :
1) Reliable Forwarding independent of registration status
2) Time based forwarding if required
3) Simultaneous Forwarding to multiple destinations
4) Sequential Forwarding (Hunting) based on rules
5) Excellent call record history
6) Call screening based on incoming Phone Number or lack of number (anonymous calls)
The correct forwarding syntax is simply
xxxxxx@voxalot.com
Outgoing calls via Callcetric are not affected.