I've been using the GotVoice (review) voicemail retrieval service for almost a year, and for the most part I've been happy with it. The free system retrieves voicemails that go to my home phone's message box and sends me e-mail links to them. Handy. On Monday, the company is releasing a major update to the service that fixes a few usability snags and adds outbound message utilities.
Current users should like the new interface. It's easier to use, and there's finally a "delete" button on each individual message.
The real action is on the outbound side. Now you can record messages on GotVoice and have them sent to any other phone, either as a regular phone call or a "stealth message" (my term for a voice message that goes straight to voicemail without making the phone ring). You can send messages to multiple users at once, even if they're on different phone networks--GotVoice understands how different networks operate. (See also: Pinger.)
Additionally, GotVoice has a nice interface for creating the greeting for your voicemail in-box. You can record a message from your computer's microphone or upload an MP3, or for a fee, construct a "celebrity greeting" from impersonated phrases. The technology is from Veritalk and is not new, but GotVoice's capability to interface with your voicemail systems and install greetings for you is pretty neat.
The company also is building a "visual voicemail" service that will let users manage all their messages from a WAP interface on a mobile phone; in other words, a poor man's iPhone. Carriers (other than Cingular, Apple's reseller for its phone) are interested in this, GotVoice CEO Curt Blake told me.
I like GotVoice because setting it up and using it requires very little work and no reconfiguring of phones. You just give it your phone numbers and PINs; and it gets to work for you. If you can stand putting in a small effort, though, I highly recommend CallWave (review) as a replacement voicemail system. I'm using it, instead of GotVoice, on my mobile phone and find it to be a better and more complete experience.
If you want to go to the next step and really get your voicemail and e-mail working together, and tie all your phones into one integrated system, then check out Grand Central (CNET.com's review; The New York Times review). It gives you a new phone number that you then have to give to all your contacts, but its capabilities are amazing.
P.S. to CallWave users: GotVoice and CallWave do not play well together. When GotVoice sends a direct message to a cellular phone that's signed up for CallWave, it goes directly to the phone's old voicemail service, not the CallWave message store.