After the Federal Aviation Administration said Oct. 31 that passengers could use electronic devices to listen to music, read and play games during all phases of flight, travelers took to Twitter to celebrate.

“Flying soon?” wrote @thegrandfinALLI. “Good news, FAA officially approved electronics for takeoff.”

But the cheers may be somewhat premature.

The relaxed rules apply only to aircraft whose cockpit equipment can tolerate radio interference signals from electronic devices, and the FAA now requires airlines to show that their planes can prevent interference before putting the new rules into effect.

A number of airlines, including Delta Air Lines, JetBlue and American Airlines, have already received approval from the FAA for all of their aircraft. But some airlines have not, and getting their fleets up to FAA standards may take some time. Policies within even a single airline can vary, if all of its planes are not compliant.

That means, in the coming months, a passenger departing from New York City could be allowed to use his electronic device during all phases of that flight, only to transfer in Chicago and be forbidden from using it during takeoff and landing on his next flight.

Sara Nelson, the international vice president of the Association of Flight Attendants-CWA, said that “the biggest challenge is this issue of inconsistency.”

“The confusion of the rules between carriers, between types of aircraft, will create a problem for flight attendants,” she said.

Flying internationally poses a similar conundrum.

The FAA is asking U.S. airlines to adopt the electronic-device restrictions of their destination and departure countries, according to Kristie M. Greco, a spokeswoman for the agency.

In Europe, for example, where the European Aviation Safety Agency prohibits the use of electronic devices during takeoff and landing on all European airlines but allows U.S. carriers to follow the FAA’s regulations, passengers aboard a U.S. carrier that meets the FAA’s standards will be able to use their electronic devices during a landing in London. But some other countries outside Europe may require U.S. carriers to respect their bans on the use of electronic devices during takeoff and landing.

Policy changes are likely in Europe. Dominique Fouda, a spokesman for the European Aviation Safety Agency, said in an email that in a matter of weeks or months the agency expects to allow the use of electronic devices in all phases of a flight, as long as they are on airplane mode.

Even under the FAA’s new rules, passengers are only allowed to read, listen to music and play games on cellphones on airplane mode. The ban on using cellphones to talk and text remains, which poses a challenge to flight attendants who are obliged to make sure that cellular services are indeed disabled.

Nelson admitted that flight attendants “can’t possibly go through and check every single device.”

“But we do call on the passengers to listen to the flight attendants’ instructions,” she added. “It’s not arbitrary. When we give that instruction, passengers should be assuming that is for their own safety.”

And on those long domestic and international flights, passengers face another challenge to using their electronic devices: power outlets. According to Routehappy, the flight data website and search engine, only about 5.5 percent of the 23,621 domestic economy flights scheduled to take off in the U.S. on Nov. 11 offer A/C or USB outlets. Those flights are on only six airlines: American, Delta, Hawaiian, United, US Airways and Virgin America, according to recent data analyzed by the company.