I'm probably missing something obvious here, so I apologise in advance!
I have a CSL pre-pay SIM, and very basic Nokia brick type mobile. When people call me it doesn't go to voicemail - just rings out until there's a recorded message saying unavailable. When I call my voicemail myself from my mobile it tells me I have no new messages, and gives me various options, including selecting a pre-recorded or personal message. It doesn't give me an option to activate / de-activate voicemail.
Anyone got any ideas?