A 911 call from a regular phone is automatically routed by the telephone carrier to the appropriate public safety answering point (PSAP), where an operator passes the call on to the appropriate police, fire, or emergency medical service, depending on the nature of the emergency. In a typical setup, the operator's console displays the automatic number identification (ANI) of the caller as well as the associated physical address. The ANI is quite different from the caller ID that appears on your phone: It's supplied directly by the phone company's switching equipment and cannot be suppressed or spoofed.
Early mobile phones had a serious problem with 911. When you dialed an emergency call, the mobile carrier routed it to the nearest PSAP -- but the decision was based on the location of the cell tower, not the phone itself. Calls often were routed to the wrong agencies, and precious time could be lost in redirecting them.
CROSSED CONNECTIONS. The problems led the Federal Communications Commission to mandate that mobile operators provide the same basic information on 911 calls that wired phones do. When fully implemented by the end of 2005, wireless 911 calls will give emergency officials both the ANI of the phone and the precise physical location of the caller.
VoIP emergency services are in a more primitive state. Some more sophisticated systems (including the Zultys ZIP 4X5 [LINK to tech21 online]) let you plug in an analog phone line and will route 911 calls through it. Of course, that requires that you maintain -- and pay for -- wireline service from the local phone company.
Vonage offers a more typical arrangement. When you set up your account, you register the physical location of the phone with Vonage. The company then uses that information to route 911 calls to the phone number of a local PSAP. But Roger Hixon, technical information director for the National Emergency Number Assn. (NENA), warns this may not get you the same level of service as a true 911 call. "The numbers [Vonage uses] may not have been cleared with the PSAP," Hixon says. "Also, the service may not have [ANI], so the callback number may not be known to the PSAP."
TRAVELING ISSUES. One of the advantages of VoIP calling can become a liability in an emergency. A service like Vonage allows you to take the VoIP adapter box from your home and plug it into a broadband connection in your office or anywhere else, in effect taking your phone number with you. Many VoIP services also let you use a laptop with a headset as a "soft" phone from any broadband connection. But unless you've registered the new location with the service, an emergency call could be routed to the wrong PSAP.
NENA is working on ways to provide better 911 service for VoIP, both for fixed locations and what it calls "nomadic" use, with at least some improvements planned for the later part of this year.
"Our goal is to provide true 911 service for VoIP," says Hixon. But until that becomes available, users of VoIP telephony should realize that emergency service may not be all they expect. Wildstrom is Technology & You columnist for BusinessWeek. Follow his Flash Product Reviews, only on BusinessWeek Online