A Group ID can be assigned to an Outgoing Line pattern to prevent conflict between common dial patterns on the same tenant or multiple tenants.
For Example:
Instead of creating two lines for a single tenant like:
8x.
8xx.
You can assign a Group ID to 8x. so that 8xx. is not required and you can have multiple copies of 8x. along with various unique options to assign to Class of Service Objects.
Here is an example of 8x. with multiple Group ID assignments:
8x.
Outgoing Line Edit|General|Group ID
After you save the change to Group ID you will see in Manager|Class of Service objects Outgoing Lines with a (x) where x displays the Group ID number.