British Airways will allow passengers to use handheld devices placed in "flight safety" mode from gate to gate for the first time from Thursday.
It will be the first airline in Europe to end a ban on the use of gadgets during take-offs and landings.
Several US carriers have already implemented the move.
Use of phones, e-readers and other electronics on BA flights is regulated by the UK's Civil Aviation Authority, which had to approve the move.
"The easing of restrictions will provide an average of 30 minutes' additional personal screen time," said BA flight training manager Ian Pringle.
"With around 300 people on a long-haul flight that will mean a combined total of approximately 150 hours' extra viewing, reading or working."
The firm had previously become the first European airline to allow travellers to power up their electronics just after landing, while its planes were still taxiing to the terminal.
However, one expert who advises Parliament on aviation issues had doubts about the wisdom of the latest move.
"This kind of activity has probably been happening surreptitiously anyway, so they are merely formalising what has been occurring - and policing it has been difficult," Laurie Price told the BBC.
"But if you are taking off or about to land in an aeroplane you should probably be concentrating on that event just in case anything were to go awry.
"If there is an incident it is most likely historically, on the evidence available, to take place either on departure or landing. Any distraction is not the best use of your time just in case you need to do something in the interests of safety."