There are two possibilities when it comes to bomb threats. The threat can be only that, a threat in which the intention is to cause terror or panic, but no bomb exists; or, the threat can be very real, in which case the bomb threat response protocol is of critical importance.
If the threat comes by phone, take notes so you won't forget anything. Try to keep the caller on the line, and have someone else call building security and 9-1-1. Take notice of background noises, whether the caller's voice is male or female, and whether it has an accent. Try to obtain specifics about bomb location and time of detonation. If the threat comes by mail or email, save the letter and all corresponding materials.
Establish a chain of command, and ensure that anyone receiving a threat knows the protocol of whom to contact if the need arises. If there are multiple companies, organizations or agencies in the building, each should have its own set of contacts.
Having an evacuation plan will help make your response go as quickly and smoothly as possible. In a multistory building, the floors immediately above and below the danger area, if known, should evacuate first. A place to reconvene outside should be part of the plan so that you can account for all personnel. Make sure a floor plan is available to police and firefighters when they arrive.