Snom ONE Technical Manual page 105

Chapter 4: Trunks
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Once the offices have been connected, the headquarters will need to dial the extension that the trunk is
routed to. Once the call hits the branch office, it will be sent to the auto attendant so that the headquar-
ters can dial the remote extensions. The trunk has to register to the extension just as a phone would, so the
system at the branch office will need to register the trunk to the system at the headquarters, the same way an
ITSP would need to be registered. Then anyone in the world can dial the DID, much like they would dial
that extension.