CallWave is about the coolest free cell-phone utility I have ever seen, and it goes a long way toward making me not care so much about the "visual voice mail" that Steve Jobs touted for the upcoming iPhone. The CallWave service, which is live now, replaces your standard carrier-provided voice mail with a much better system, and it lets you pick up incoming cell-phone calls on any other phone or even your PC.
I've been using the competing GotVoice service since I first wrote about it in May to get my cellular and home voice mail messages via PC. But CallWave goes well beyond GotVoice. Both can alert you via e-mail when you receive a new message and then play the message over the Web. But while GotVoice is a hack--it periodically has to dial your voice mail to collect the messages, which introduces an unpredictable delay into the alerts--CallWave is a replacement voice mail service. Once you program your phone to use CallWave instead of your carrier's voice mail (instructions are provided when you sign up, and they're simple), CallWave intercepts all calls you don't answer. When you get a message, it sends your cell phone a detailed SMS with the name and number of the caller, and the duration of the call. It also sends you an e-mail with a Web link to play the message; optionally, it can send messages to you as e-mail attachments.
The only disadvantage when compared with GotVoice is that CallWave only works on cell-phone voice mail, and only supports one number per free account; GotVoice will also handle landline voice mail, and it can handle multiple systems per account. I'm still using it for my home phone voice mail. In addition, with CallWave, you lose the use of your phone's message indicator.
There's a CallWave Windows application with additional powers. When a caller leaves you a message, one option is to have the application play it immediately on your PC. If you want to call the person back, CallWave will call one of your phones (landline or cell) and then connect you to the caller. It can also turn your PC into a VoIP phone and return the call that way (this feature is in beta, but it worked great for me). You can also send the caller an SMS directly from the application.
You can even use the application to answer a call while someone is leaving a message. If you press the "take call" button while the caller is either listening to your greeting or recording their message, CallWave will tell them you want to talk to them and then call the phone of your choice (or your PC) and connect it to the incoming call. This feature makes it easy to continue to use your cell-phone account when your cell phone is turned off or out of reach.
Though I doubt that CallWave was designed for it, you can use its call-connection service to make free long-distance calls (I couldn't get it to work for international calls, though; for that see TechCrunch coverage of AllFreeCalls.net). CallWave acts as the middleman, placing calls to your phone or PC and to the person you're calling. If you're on a landline, the call is essentially free. I look forward to the day when CallWave also interoperates with Skype.
CallWave is full of other well-thought-out features, and it genuinely makes your cellular account more useful. The fact that it's free blows my mind. There's a paid version as well ($9.95 a month) that lets you listen to voice mails as they are being left. The company also offers other paid telephony services.
Did I mention how cool CallWave is? OK then.