Last week, I started testing CallWave Mobile, a free service that replaces your voicemail service and sends copies of messages you receive to your email inbox.

Setting up the service the first time only takes a minute. You just sign up for an account on CallWave's site, and enter a code on your cellphone. The code is carrier-dependent, and CallWave tells you what it is. Once that's done, all unanswered calls are automatically forwarded to your CallWave inbox instead of your carrier's voicemail service.
CallWave Mobile Widget
When you get a new voicemail message, CallWave notifies you via SMS, email or both (this can be configured in your account settings). These notification messages include the caller's phone number, the time the message was received, the length of the message, and a link to a webpage that plays the message directly in your browser if you're at a computer. You can also get messages as audio clips attached to the email notifications, if you like. CallWave provides handy visual voicemail widgets/gadgets for both Windows and Mac OS X as well.

If you're at a computer, you can respond to voicemail messages by either sending the caller a text message from the web page, or initiating a call back. In the latter case, CallWave dials you and the caller and connects both of you together.

Deactivating the service is as simple as setting it up. You just punch in another code (which CallWave provides you with as well), and you can continue using your carrier's voicemail service.

I find this service quite handy because there are places where I don't get cellphone reception. Many of the computer labs and classrooms in the engineering building on campus, for example, are dead spots, but I'm almost always near a computer at these places. If someone's trying to reach me, I can at least listen to their messages and respond if it's something important. Plus, there's really nothing that your carrier's voicemail service does that CallWave can't, so you don't lose anything by using it.

My experience with it has been good so far - it was quick and easy to set up, and notifications come in almost immediately. Check it out if you think it might be useful to you. :)