I can turn off voicemail, but unfortunately that's not a sensible option - I need the NHS and the local gov't to be capable of leaving me messages, and voicemail seems to be the only way they're willing to do that. (I *have* left lectures and supervisions to take a medical call, but I am not always by my phone, so.)

As for the reason... well, I couldn't think of a suitably professional way to say "if you leave me voicemail I will probably avoid my phone for at least a week, delaying my calling you back, so Please Just Don't" ;)