All prepaid and postpaid plans automatically include voice mail. But we should be able to opt out, since spammers and scammers can call and use up minutes on the plan leaving voice mails, and it also costs money to retrieve them. Nobody legitimate ever leaves me voice mail anyway, and I should be able to permanently disable it from self serve if I so choose.
(I've seen ideas for 'workarounds' like recording an extended greeting or leaving the mailbox full. Neither of those work all that well. This is a feature that really should be optional.)