I call 303-632-4200 for Denver Service (then select option 2). My success rate is 50% — every other call is picked up (I call during normal business hours, of course). Once when there was no answer I tried to leave a message only to find that the voice mailbox was full. Haven't tried that again. When I do get a service rep on the line I find him or her pleasant to deal with.
I'm due for a DU replacement on Wednesday. The replacement DU was supposed to arrive three weeks ago but I heard nothing. Finally called again on Friday and they found a DU for me (from someone else?) and I was able to schedule an appointment right away. [Sure hope that it is a "Q revision" DU, not one of the earlier ones, forgot to ask.] I was hoping to have this work done in September before having to deal with snow crossing the mountains. As it happens, a statewide snowstorm is predicted for tomorrow...