So I called my cell carrier - AT&T wireless (AKA:Apple Wireless) and see if there was something messed up when I had them switch the account over to my new phone. A couple of months ago I went from a 5 year old AT&T/Cingular/HTC 8525 to a Google Nexus One. I explained the issue and asked if the agent would check to see why I've been getting many missed calls w/ no voice mail left lately. The agent checked my account and saw that the "ring time" before VM picks up was to zero (never transfer to VM) on my account which causes the incoming call to ring until I pick it up or the network sends it to the "the subscriber could not be reached" message.
Moral of this story is:
if you're on AT&T; call your cell;
if you can leave a VM - good,
if not - call customer service and have them check your voice mail settings.
I asked the agent why / who would have changed the setting on the account, she said, that it may have been an oversight on the part of the agent who did add/replace on my new phone's IMEI and that the old phone may have handled incoming no-answer different than the new phone. She apologized several times and applied a good-customer credit to my account and thanked me for using them as a carrier. I asked that she call my cell and leave me a VM so that we could be sure that the changes took effect and so that I could see of the message waiting indicator came on. Both worked well. The VM indicator looks like the 1980's reel-to-reel tape deck (TEAC X-10R) that I have at my parent's house. The indicator also looks a little like a DEC PDP-11's DECTape device, except with the reels above the heads...
This was a good customer service experience and I got a credit for my trouble. I would have preferred to not have had the issue in the first place, but then, I didn't get my Nexus One from AT&T, so they probably don't have any pre-built set of parameters that they could apply to my phone's account as they probably did for the 8525. I got the phone direct from Google in the last shipment before they stopped selling wireless phones direct to the public...