The “big four” accountancy firm PricewaterhouseCoopers is to remove all landlines from office desks by the end of the summer, reflecting a shift to mobile phones.

PwC, which has 24 offices across the UK employing about 18,000 people, said the shift to a “mobile first” culture made sense in the modern working environment.

A handful of landlines will remain in use for security teams, reception and some client meeting rooms, but by the end of the summer all staff will be mobile-only.

Emma Thorogood, PwC’s London director of communications, said the shift had begun a few years ago during the refurbishment of the company’s Leeds offices, when it was decided landlines were superfluous.

“This programme … is now being rolled out across each of our campuses,” Thorogood told the Guardian.

“It is all about changing working practices – staff are a lot more agile and flexible. They may be working for clients or working from home. And offices are now more open-plan, and with hotdesking the use of landlines is something we just don’t do any more.”

Businesses across the UK are increasingly moving away from landlines. In 2010, UK firms had more than 10m landline numbers, but by the end of last year that had fallen by 35% to 6.4m, according to the communications regulator Ofcom.

The time spent by businesses on landline calls has halved, from 38m minutes in 2010 to just under 19m last year.

“With landline usage falling rapidly, we believe that a more mobile-focused policy is a more efficient way of working and supports our people’s increasingly flexible working style more effectively,” said Thorogood.

Residential use of landlines has also dropped markedly, although most households still need to pay for one to access broadband. In 2010, UK homes made landline calls totalling more than 90m minutes, but that had fallen to about 35m minutes last year.

In March, Ofcom forced BT to cut the cost for customers who have a landline but no broadband by £7 (about 37%) a month. The £84 annual saving will benefit mostly older customers who do not use broadband.

