Earlier this month I had the unhappy experience of using the iPhone app VoiceMail.[ App Store link] The U.S. $0.99 app was designed to send an audio message to another iPhone, or a PC or Mac. It failed almost every test I gave it, but the developers say they have been hard at work and have updated VoiceMail.
In my tests I have found the app to be much improved. The audio is no longer distorted, and the message plays back on any PC now. QuickTime is no longer required to play back the message, as it can come as a standard MP3 file. Uploading the message from the iPhone is still pretty slow, even using WiFi. A short 5 second message took 15 seconds to send.
This is a handy utility if you want to send an audio message and don't want to use voice mail, although it seems pretty useless for iPhone to iPhone messaging as you already have voice mail available.
I'm glad to see this app updated, and for some it may be very useful. It's clear it works now, but with MMS messaging coming in iPhone OS 3.0 and a Voice Memo app that may allow forwarding the sound file, the features of VoiceMail may be overtaken by the Apple update.
It's not a big risk for less than a buck, and I was glad to see the developers respond so thoroughly to my earlier review and fix most of what I complained about. If you have use for the features it offers, and can live with some uncertainty about privacy, you can certainly give it a try.