I realized today that I've been using CallWave as a visual voicemail service for the past few months and haven't even looked back to switching to normal cellphone voicemail; the reason I relaized this was I observed one of my colleagues attempting to check his voicemail int he traditional manner of hitting a speed dial, entering his password, and navigating the voicemail tree.
You can liken the use of visual/e-mail-based voicemail to the paradigm change that people experience when they first use TiV: it entirely changes how you interact with a traditional service. CallWave's voicemail translation service isn't great, but for the most part I can get the gist of the message without ever having to listen to it. In addition, I like the fact that the caller ID data included with the e-mail from CallWave is more detailed; I only have a few people that actually block their caller ID when they call me, so it's nice to see the caller location (i.e., my dad in San Francisco blocks the caller ID on his cell phone, but CallWave tells me that "An Unknown Caller in San Francisco, CA" called, so I know it is him).
The OSX visual voicemail widget is pretty useful, though I try to be away from my computer enough that I really use the e-mail functionality a lot more than the widget. I have CallWave send the e-mail with the WAV attachment to my Gmail account, which immediately gets pushed via IMAP to my Blackberry; the internal audio player on my Pearl handles the WAV file attachments with no problems.
CallWave is free during beta and I think that the visual voicemail and e-mail portion will remain free as I can only really see them trying to charge for the voicemail to text translation service (if they can make it much more accurate). I recommend any sort of visual voicemail solution to anyone that uses an e-mail enabled cell phone with the capability to play WAV files.