Telephone customers who use the relatively new Voice over Internet Protocol technology to power their phones need to understand how 911 dialing works. If they don’t, they’ll lose their phone service, according to the Federal Communications Commission.

Here’s the reason: In the past, when emergency calls were received by 911 call centers from VoIP lines, the operators had no information as to the whereabouts of the caller. Unlike traditional landline phone service, which attaches detailed location information to all phone numbers, VoIP lines have no information. In the case of an emergency, when callers sometimes cannot give his or her location, this information is crucial to saving lives.

That’s when E911 for VoIP was introduced to solve the problem. (It stands for, “Enhanced 911.�) It allows VoIP phone numbers to contain the same location data as regular phone lines do, but there are a few kinks in the system.

VoIP phone service is powered by the internet, so there’s no way to tell exactly where the VoIP call is coming from. The location data, therefore, has to be entered in by the user. This raises a problem, however. VoIP lines are portable; if a customer moves from, say, Minneapolis to New York City, and does not update their address with the system, serious problems can arise.

Not only will a Minneapolis 911 call center be called if the customer dials 911, but the call center will be given the customer’s previous address. (Dispatching police incorrectly to a Minneapolis residence, for example). It is for this reason, that the FCC wants all customers to understand how E911 works.

And, if they don’t acknowledge their understanding, they won’t have phone service. It’s that simple, says the FCC. To date, an estimated 100,000 VoIP customers still have not acknowledged their understanding – which prompted a move by the FCC last week.

The FCC said on Friday that it is extending a deadline, which used to be today, to September 28 to give VoIP providers more time to contact their customers.