The U.K.'s phone regulator says it will keep thousands of the nation's famous red public phone kiosks in service, despite a sharp drop in calls from the boxes.

Communications regulator Ofcom says the payphones are still vital in case of emergencies, and in areas where cellphone users can't get a reliable signal.

Under the regulator's new criteria, a call box will need to be used at least 52 times over a 12-month period for it to stay in service. And if a kiosk is in an area identified as an accident or suicide hotspot, it can't be removed.

"Some of the call boxes we plan to protect are used to make relatively low numbers of calls," said Selina Chadha, Ofcom's director of connectivity. "But if one of those calls is from a distressed child, an accident victim or someone contemplating suicide, that public phone line can be a lifeline at a time of great need."

As Ofcom revealed its plan to protect the kiosks, it acknowledged that 96% of adults in the U.K. now have a cellphone, and that mobile phone coverage has gotten much better in recent years. The new criteria for taking a phone booth out of operation include a stipulation that its service area must be covered by the U.K.'s four mobile networks.

Even if a red phone kiosk is slated for decommission, it can be adopted by its local community under a plan that lets governments or organizations buy the call box for just £1. According to Ofcom, "more than 6,000 kiosks have been converted to a range of different uses, such as community libraries, or to house life-saving public defibrillators."

Red call boxes that meet the new protection criteria will still face a reckoning, because the U.K. is migrating its analog telephone network to be fully digital. With the old phone system set to be turned off by the end of 2025, call boxes that survive the cut will need to be upgraded to Internet Protocol standards.

The U.K. currently has around 21,000 public call boxes. Ofcom says they're frequently used for urgent calls: "Almost 150,000 calls were made to emergency services from phone boxes in the year to May 2020, while 25,000 calls were made to Childline and 20,000 to Samaritans."