Business Group lines access the standard dialing plan and external calling by using an External Line Code. There is no default value for this code, but 9 is the standard number used. Business Groups can also be configured to recognize external directory numbers without the External Line Code (known as Assume 9 dialing).
To dial an outside line you simply dial 9 and then the number (9-XXX-XXXX, 9-1-208-XXX-XXXX)
An example of a recognized external directory number would be 911.