Not only China Post is doing a bad job (see post below), but also China Mobile is not performing the way it should. Recently I suddenly had three voicemails. A bit strange, considering that my phone was on the whole time, and I normally have maximum one voicemail per day. So I listened to them and realized they were at least several days old! One was actually quite urgent, and the caller must have not been happy with me not getting back to him about it. Later that day I was talking to a business relation in Europe, who did not get back to me on some questions. He told me he left me a voicemail about them about a week ago. I never received that voicemail!
This is getting to the point that their unreliability might jeopardize business deals. I now consider switching off voicemail on my mobile, and getting a Skype phone number with voicemail (problem: no Chinese numbers available yet). Not the best solution, but better than not receiving voicemails! Who knows what other calls I might have missed?