I think a combination of mobile and internet telephony has made the desktop phone redundant – that and messaging services etc. For that matter, I've not used an answering machine for years, I turn them off.
I have a phone on my desk that I use on the rare occasion I have to make phone calls, simply because my ability to understand people on the phone is greatly improved by not having the GSM codec throwing away half the audio, and this way I can at least force g.711 on my leg. (Still stuffed if the other party is on a mobile, or a lowest-bidder VOIP connection to Elbonia, of course.) Life's too short to use a PC to make phone calls, and while Android's native implementation seems to work pretty well
[1], it would involve streaming realtime bidirectional audio over The Devil's Radio, which is asking for trouble when you live somewhere where the WiFi band is so congested that it would give the Daily Mail cancer.
Voicemail exists so that the receiving telco can accumulate the call termination charges. A few pence here and there soon covers the cost of recording messages instead of giving a busy signal or letting it ring out. It's basically useless in the real world, as it's the least convenient way to give someone a message, even if people knew how to speak properly into answering machines (a skill which went out with waiting a decent amount of time for people to answer the phone). Caller ID makes it mostly redundant anyway.
That said, I do have voicemail configured on Asterisk for automatically redirecting unknown callers who fail the Turing test to, just in case someone who doesn't have the sense to use email from a large bureaucratic organisation that doesn't present CID needs to get in touch.
[1] When not nobbled in the firmware, because mobiles tend to be sold wholesale to telecoms companies.
