I have been using a service from Callwave for a few weeks now.
It provides a replacement voicemail system for my
mobile cell phone with a range of really useful services.
It has a Windows Vista Sidebar gadget that hooks up to your voicemail and lets you listen right from your desktop.
Plus, it has a voice to text feature which sends an email with the gist of the message, so that you can see any keywords and decide if you want to listen to it.
I really like it - it's like having a personal assistant screening all your calls.