After a decade of wrangling between government and the wireless industry, there's still no certainty that when a cell phone is used to dial 911 an emergency dispatcher will automatically know the caller's location or phone number.

Now, with the rise of another new telephone technology, Internet-based calling, officials appear determined to avoid a repeat of that wireless experience, as well as recent incidents where 911 calls from Internet phones went unanswered.

So on Thursday, the Federal Communications Commission is expected to set a firm deadline for providers of the new service - known as VoIP or Voice over Internet Protocol - to deliver the same 911 capabilities as regular phones, the vast majority of which can be located in a crisis.

The expected order, which may allow as little as 120 days for compliance, would follow months of finger-pointing and bickering between VoIP carriers and the traditional local phone companies who own the network connections to the nation's nearly 6,200 "public safety answer points."

"It's an aggressive time frame, but from a public policy standpoint it's understandable why the FCC is being aggressive," said Carol Mattey, a director in Deloitte & Touche LLP's regulatory practice who was deputy chief of the FCC's wireline competition bureau until January.

"The whole wireless 911 mandate just dragged out and dragged out, and policy makers may want to make sure it doesn't get dragged out like that for this new technology," said Mattey, noting that 911 became an issue after many cellular networks were built. "In the wireless situation, you had a whole industry up and running and you had to retrofit systems to make it work. The VoIP industry is relatively in its infancy, so lets make it clear from the beginning that you need to provide 911 rather than going back and jury-rigging something."

It was only with the promise of intervention by new FCC Chairman Kevin Martin that sharp rhetoric has given way to a somewhat more cooperative tone by the opposing camps.

Naturally, both sides are hesitant to sound a politically incorrect note when it comes to public safety issues. Yet there's been a barrage of anxious lobbying at the FCC.

Internet phone carriers, ranging from mainstream leader Vonage Holdings Corp. to hip innovator Skype Technologies SA, are worried the FCC order may stifle the industry's development and ability to compete. In its talks with the FCC, AT&T Corp. cautioned it may need to disconnect certain subscribers to its VoIP service, CallVantage, if the order doesn't allow enough time and flexibility to deploy enhanced 911 services.

The Bell and smaller local phone companies have argued that VoIP providers can easily pay them like any other rival to connect most of their customers to the 911 system in a matter of months. Some local carriers, led by SBC Communications Inc., have complained that Vonage has rejected that solution as a quick first step, insisting instead on new, customized technologies.

It is unclear how the FCC order will approach two unique features offered by VoIP technology: the opportunity to sign up for a "local" phone number from a distant area code, and the ability to take a home or office number on the road and use it from just about any high-speed Internet connection in the world.

These nomadic features present a challenge for the 911 system, which was developed decades ago for a telephone network where area codes and phone numbers were linked to specific physical addresses.

One factor undercutting Vonage's emphasis on deploying a new 911 technology that reflects the needs of roaming customers is that such users represent a tiny fraction of the fast-growing VoIP market.

Roughly half of the nation's 1.5 million or so VoIP users are served by cable TV companies who already provide full-blown 911 capabilities because they only offer phone service to a fixed location.

For the other half of these VoIP converts, the main allure of Internet phone service appears to be savings, which can range from $20 to $50 per month for an unlimited national calling plan.

Given that financial incentive, it turns out that only about one in 20 subscribers to non-cable VoIP services take advantage of the roaming capability, according to AT&T and other providers. The rest use their VoIP lines in one fixed location.

For cable companies, connecting their fixed-location customers to the enhanced 911 system was relatively easy.

But most of the non-cable VoIP providers have only been able to offer a watered-down version of 911 service that often directs emergency calls to a general administrative phone number at a local public safety office. In many cases, those lines are not staffed by emergency operators, and may even just play a recording or go unanswered, particularly during non-peak hours.

This approach has drawn sharp criticism, as well as lawsuits by two states against Vonage. New York City officials have been particularly vocal, telling the FCC the current practice is "hazardous and unacceptable."

The shortcomings of this system were exposed prominently earlier this year when Vonage customers in Texas and Florida had trouble getting through to 911 during emergencies.

Amid the negative publicity, Vonage recently reached a deal with Verizon Communications Inc. to connect directly with that company's enhanced 911 network in a way that calls will go to the appropriate emergency dispatch center along with an address from which the call originated. The new system is expected to debut this summer in New York City.

AT&T, meanwhile, has started using its own local phone facilities to connect its VoIP customers to the enhanced 911 system.

One complication for VoIP carriers is that they may need to make separate arrangements with many of the nation's more than 1,000 local phone companies, or at least an intermediary who has done so.

Another challenge, depending on the reach of the FCC order, will be delivering enhanced 911 to mobile VoIP users. For now, such users will need to update their location with their carrier every time they move to ensure a 911 calls goes to the right emergency operator.