This evening, before going grocery shopping, we stopped by the Verizon store near Safeway where I bought my mobile phone. The headset had started acting up. They looked up my record and found that it had been just less than a year since I bought the phone and accessories, so the headset was still under warranty. The sales person was bemused by my having a headset that didn't just hang out of my ear like a Borg implant. My earphone is on a full headpiece. I find the hang-in-your-ear connections uncomfortable. Fortunately for me, they found another one of the now-discontinued headsets and gave it to me.
Before leaving, I plugged it in and called Cheryl. While I could (sort of) hear her, she couldn't hear me -- standing across the showroom floor, she could see my lips moving but could hear no sound. So it appears the problem wasn't actually the headset, but the telephone. We returned to the salesman. He seemed unhappy to have to deal with me. I assume that he doesn't get commission for dealing with replacements like this, but I've been paying the small extra amount for a service plan that includes free replacement if the phone breaks, so he did need to do something.
Amazingly, they had another mobile phone of the same design as mine. I say "amazingly," because it sure seems to me that mobile phone models are discontinued approximately once a week, so that none of the phones actually in the supply chain pipeline are actually in production anymore.
After patiently waiting for the salesman to find my replacement phone and get my address book changed over, I tested it with the new headset, and everything worked. He even said I could keep the new headset, as it was a discontinued model anyway and not worth his time to try and un-exchange. So now I once again have a working phone and headset, although it looks like the next time the headset has to be replaced I will be forced to be assimilated.