You said "3 of my many phones". Are there phones on the same system that have not experienced this issue? Have you tried one of these working phones into the same port? You say it does not always happen.

If the problem was due to programming the symptom would be consistant.

My guess is a hookswitch issue, even though the 3000 series was not known for that like the 2000 series was. Pretty sure the hookswitch has 2 circuits in it. 1 for control of data and 1 for control of audio. The audio contacts may be intermittent and performance will vary according to humidity.

Also, on received calls, these should be no delay due to inter-digit timeout like on outgoing calls. Make sure that you are not receiving the call based upon a transfer from your auto-attendant that is using supervised transfer. That will cause an answer delay due to it waiting to see that you answered and waiting for the "A" tone to be sent from the VM to the KSU.

"The difficult we do immediately. The impossible takes a little longer"