Call it the "one number to rule them all" service. Google Voice, which goes live in a few weeks, is supposed to let friends, relatives, and business contacts find you whether you're at your desk, on a business trip, or vacationing in Peru. Tests carried out over the past few days suggest that, despite a few glitches, it could well live up to this promise.

Users will soon be able to register, sign up for a phone number in a local area code, and add multiple landline and cell-phone numbers to an account. When someone calls a Google Voice phone number, all the registered phones ring at the same time.

The service takes several telephony technologies--voice-over-Internet Protocol (VoIP), voice transcription, and call routing--and connects them to the Web. Other Internet phone services let you play voice-mail messages on a computer or record calls, but Google Voice is a step towards unified communication. It's the voice equivalent of an e-mail address. Once you register a number, the idea is that you never have to worry about which phone you are using, even if you switch offices, homes, or cell phones.

Google Voice doesn't actually host phone calls. Instead, when you make a call, the service calls your own phone, and then dials the number you want. Like other Google services, it taps a vast cluster of computers to offer extra services, such as voice mail and call recording. Because it is entirely IP-based, the service is always "on the line," meaning you can access it at any time, for example, by pressing 4 to record a current call.

"The extra piece of equipment is a VoIP gateway, which interconnects the PSTN [a standard telephone line] and SIP [the digital line] services. I would expect their data centers will have large racks of these," says Rob Enderle, founder of the research company Enderle Group. "Google Voice translates an SIP address into a phone line, converting the digital data stream to an analog stream and then allowing the line to connect."

Time delays, also known as latency, remain a serious problem with VoIP, but if any company can handle tremendous call volumes, expand computer clusters quickly, and reduce latency issues, it is Google.

Google Voice is also largely about unification. No matter which phone you use, there is one portal for all voice-mail messages. You can play them on the Web, save them as MP3 files, and even post a voice-mail message on a website using an HTML embed feature. Conference calls are also easy: just answer an incoming call to add it to the current one.