An In-Building Communications system is disclosed which permits communication in tunnels, underground parking garages, tall buildings such as skyscrapers, buildings having thick walls of concrete or metal, and/or any building which has communication dead zones due to electromagnetic shielding. The invention includes a portable bi-directional amplifier (BDA) system, an outdoor antenna system attached to the building or independently mountable, an indoor antenna system attached to the building or independently mountable inside the building, and a standardized, In-Building Communications (IBC) interface box affixed preferably to the exterior of the building. The interface box communicates with antenna systems attached to the building. The fire department or other emergency response personnel carry portable outdoor and indoor antenna systems and a portable, lithium-ion battery powered, bi-directional amplifier (BDA) system which may be connected to the building during an event such as a fire, earthquake, or an act of terrorism or whenever radio coverage enhancement is required. The portable BDA system is simply connected to the standardized, IBC interface box and powered thus restoring communications within.