The UK telecoms regulator on Tuesday outlined proposals to save thousands of public telephone boxes from closure, despite near blanket ownership of mobile phones.
Some 96 percent of UK adults now own a mobile phone, while signal coverage has improved across the country, changing the way people make calls.
But Ofcom said that as operators assess which public call boxes to decommission, "clearer, stronger" rules were needed in places where they are still a lifeline.
It said some 5,000 phone boxes would be protected from removal if they are deemed vital to local communities where mobile network coverage is poor.
Other criteria include if they are at an accident or suicide hotspot; if at least 52 calls have been made in the last year; or if they have been used to call helpline numbers.
Ofcom's director of connectivity, Selina Chadha, said: "Some of the call boxes we plan to protect are used to make relatively low numbers of calls.
"But if one of those calls is from a distressed child, an accident victim or someone contemplating suicide, that public phoneline can be a lifeline at a time of great need."
There are currently some 21,000 public phone boxes across the UK.
Operator BT is responsible for the older red phone boxes and their modern counterparts, while KCOM operates the cream-coloured kiosks found in Hull, northern England.
In the year to May last year, nearly 150,000 calls were made from them to the emergency services, Ofcom said.
In the same period, 25,000 calls were made to the children's counselling service Childline, and 20,000 to suicide prevention charity Samaritans.
Overall use of public call boxes, however, has fallen in the last two decades, from about 800 million minutes in 2002 to seven million minutes in 2020.
In recent years, more than 6,000 decommissioned red phone boxes have been converted into community libraries or to house defibrillators.