to the BB. Please enjoy it. Now as to your question.
If you use the system call forwarding it will tie up two lines (one in and one out) and can produce low volume, depending on the line conditions.
Do you have call forwarding on your main number? If you use the telco call forwarding, you do not have the combined line loss.
If you do want to do the system call forwarding, please PM or e-mail a Mod in this category as this is more than user guide information.
Good luck and Happy New Year.