Phone number availability is very good, even in remote areas. During Technology Review's test period, there were never any connection problems, even with Google Voice originating calls from Google data centers. Enderle says there may be issues with reliability in the future, noting that Gmail does not have a great reputation for being available at all times.

When a caller leaves a voice mail, Google Voice automatically records and transcribes the message, then sends the transcription to you via e-mail. The transcription service uses technology developed originally for voice search. Enderle notes that the voice-recognition service has a hard time with accents and ambient noise, and does not interpret local vernacular--words not found in the dictionary--accurately. In our tests, most transcriptions were about 50 percent accurate--the service missed common phrases such as "checking in with you" and failed to understand some city names and more-technical words, such as "convergence." The speech-to-text engines employed will likely improve over time. One complaint: you can record incoming calls, but not placed calls. And recorded calls cannot be transcribed--transcription only works for voice mail.

Google Voice lets you send and receive text messages--again, by routing them between existing carriers. You can view a list of every SMS message you have ever sent, which is a highly useful feature. It's easy to review a history of placed, missed, and recorded calls. You can also import contacts from various address books. And you can easily disable one or more phones using a feature called Do Not Disturb.

Google Voice has room for improvement, of course. You can't "daisy chain" phone numbers so that the service tries one number, then another. Security is another potential issue. Recently, hackers showed that a caller could use Google Voice to tap into the services on a cell phone by spoofing the codes used to identify calls and messages sent over the Internet. Sara Jew-Lim, a Google spokesperson, says the company plans to add a default PIN to Google Voice; currently, a PIN is available only as an option.

Overall, Google Voice is worth considering for anyone who wants to view call transactions on the Web, uses multiple phones during the day, or needs to record phone conversations. It's a handy way to unify all voice communication, while trusting that the number you pick today will be yours for years to come.