Unfortunately for this case, the tools that are available in the IC platform to open mail folders do not currently support opening Public folders.
Could you possibly create a generic user mailbox to send the messages to, rather than a public folder? That mailbox could forward copies to the Public folder with an Inbox Rule.
The downside to this possible workaround is that the two message stores will not be in sync. So, if you were to listen to a message through the TUI, then visit the Public folder from your desktop, that message would still be a new, unread message.
Perhaps some more detail on how your users interact with the voicemails would help find a solution. Do they use the TUI only, TUI mostly, PC mostly, etc...?
Thanks!