Group pickup allows devices to pickup incoming calls that are directed at accounts (other than their own) belonging to the same customer.
The above screenshot hightlights the location of the following two fields:
Group Pickup: Boolean field, used to determine whether this feature is enabled for this particular customer
Group Pickup Prefix: The actual number that is to be dialled by accounts wishing to accept the incoming call
Note: if you are using standard dialling rules, you will need to add your chosen Group Pickup Prefix to the list of exceptions.