Mark Siegel, a spokesman for AT&T Wireless, said large spikes in call volumes after emergencies or other events will always cause some callers to experience difficulties in getting their calls through. As an alternative, callers should try sending short text messages, which use less capacity on the networks because they pass through in bits and bytes instead of requiring a dedicated circuit as a true phone call does.

Roger Entner, a telecom analyst and senior vice president of the communications sector at New York-based IAG Research, agreed that mobile phone carriers can't feasibly build networks that can hold up under every conceivable emergency and allow every call to go through.

"If you live in an unlimited resource world, it's certainly possible, but we don't live in an unlimited resource world," Entner said. "The wireless system is not advertised as the system of last resort. Nobody ever made the claim that this system will work always."

Emergency first responders have mobile phones that use codes to automatically route their calls to the highest priority to ensure they get through, Entner said. "Those safeguards are in place," he said. "Yes, we are being inconvenienced in an emergency [when our calls can't get through]. I think people should be able to accept that."

One problem in building more capacity for emergencies, he said, is that the wireless companies don't know where emergencies will happen, so they have no way of building in the extra capacity ahead of time since mobile phone users are, well, mobile. With wired phone service, the phone companies already know where the service demands are because people and businesses are in fixed locations.

Wireless carriers know that an NFL football game will boost capacity needs at the stadium because of the 70,000 fans in attendance, and the carriers can bring in portable equipment to bolster the capacity temporarily, Entner said. "In a disaster, you can't anticipate that."

Jeff Kagan, an independent telecom analyst in Atlanta, also said it's unrealistic to expect that mobile phone companies can make their networks big enough to withstand occasional high-volume needs.

"It's a constant balancing act between having the capacity but not having too much capacity so that you have to charge customers more and be uncompetitive," Kagan said.

Another analyst, Ken Dulaney of Stamford, Conn.-based Gartner, sees it differently, however.

Today, mobile phones have become so "mission critical" for users that new ways need to be found to make them work more efficiently during emergencies, he said, even when the networks are overloaded. In many homes, he said, wired phone service is no longer used, making cell phones or VoIP phones the only means of telephone communication. If the power is out, VoIP phones won't work, making cell phones even more important, he said.

Dulaney said alternatives, such as metering cell phone use in emergencies so that all users can get some time to make their important calls, need to be reviewed. Another alternative is a callback service, like those used in the 1950s, where if a circuit is busy, the customer gets a phone call back when the circuit is available to make a call, he said.

"I think it's going to require government regulation" in the future to make it equitable, he said. "This sort of rationing of calls is the only way to take the existing [network] capacity and let people use it. You've got to go to a rationing mode just like in any emergency."