What version of CallManager are you running including service packs? Basically you
receive a "Bandwidth" message if you have run out of available bandwidth configured for
your location. Go to System > Location to determine the available bandwidth allowed
for calls from other locations to this device's location. You can check a device's
location by going to Device > Phone. AAR can also be configured in your voice network
if you are running Version 3.3.3 and later. AAR allows the call to be re-routed over the
PSTN if there is no available bandwidth.