Understandable, it might be worth a couple of hours of research to see if it is even feasible. I've read several threads on different Treo sights where people are looking for this function. For some stupid reason the Treo only gives one notification of a voicemail. There are a few programs, like Butler, that will remind you until you clear the reminder. However the voicemail indicator stays on and there are no further indications you have a voicemail. If you clear the initial alert until you turn the Treo on you won't see you have a voicemail. I personally have had that be several hours. There are a bunch of people looking for this function and to date I haven't seen a satifactory solution. It might give you an edge if you can tap into this control and monitor it.
Here is what I would like to do: Watch for the indicator to be on. If it has been on for 30 minutes alert me every 5 minutes until I clear the alert. If it stays on for another 30 minutes alert me every 5 minutes until I clear the alert.