Group pickup allows devices to pickup incoming calls that are directed at accounts (other than their own) belonging to the same customer.

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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.