Hi commtech,
From your response I see that the CO is placing the call on the trunk and because of whatever is failing the calling party hears nothing, hence the 'dead' condition. You may need to test all the DID trunks to verify which ones are working and not. With the dead condition if the calling party stays off-hook does it ever give a fast busy or just nothing? If a fast busy, is it from the CO switch or the Legend? What I'm getting at is to isolate the problem. If transmission is impared then NO digits will get thru! The Legend is 'looking' for digits to be sent when the DID trunk is seized, if none or partial it will timeout, hence failed call attempt. Perform tests from my previous response and you should be able to isolate the bad ones. Also sometimes the CO switch will put DID trunks on maintenance busy, because of conditions the switch might see, so if you find any you can't land with a call, first test the Legend, if OK then open a trouble ticket with the Telco or service provider. They should provide cooperative testing and you can request it.
Good luck!
JIM