Short excerpts from the radio calls.

First Tower Collapses (1 min.)
Second Tower Collapses (2 min.)
The Rescue of Capt. Fuentes (1 min.)

Planes have crashed into both towers and the tape picks up minutes before the collapse of the first tower, includes the collapse of the first tower and the response immediately after the collapse. (15 minutes)

Tape 1: Before, During and After The Collapse of the First Tower

After the first tower collapse, there were reports of people stranded in the subways under the World Trade Center. (4 minutes)

Tape 2: Checking Reports of Passengers Trapped in Subway Cars

Just as some officers are accounted for after the first collapse, the second tower collapses. (9 minutes)

Tape 3: Before, During and After the Second Tower Collapse

As calls come in from people, officers and firefighters trapped, emergency services workers try to keep them calm as they pinpoint locations. Tape includes call for help from Capt. Fuentes who was pulled alive from the wreckage. (9 minutes)

Tape 4: The Search and Rescue Effort

Units of officers and firefighters set up command posts around the area but staying in contact proves difficult. (17 minutes)

Tape 5: The Mobilization Continues

Warning

"These emergency radio transmissions are unedited and contain disturbing content"

Source for these are from: Robert Sanford/ http://www.bayscan1.50megs.com/
Initial communications from the NYFD during WTC incident
Initial communication from NYPD Emergency Services and NYFD
Additional NYPD Communications from WTC incident