The outage wreaked havoc across Britain, with millions of drivers unable to use navigation apps and customers not having the option to use their phones to make in-store purchases.
In London, electronic boards announcing the arrival times of buses went dark while Uber drivers complained of being unable to pick up new orders.
Telefonica, the Spanish owner of O2, said more than 12 hours after the outage was noticed in London at around 5am that it had been assured by Ericsson that “full service will be restored for customers by (Friday) morning”.
O2, which has 25 million customers in Britain, also has another seven million people whose mobile providers “piggyback” its network.
SoftBank added that its customers had faced a near five-hour outage “caused by Ericsson-made software errors related to its packet switches, covering our customers nationwide”.
The Japanese company also cited an Ericsson report that indicated that telecom carriers in 11 countries were hit.
In Stockholm, Ericsson added it was taking “immediate action”.
“Ericsson has identified an issue in certain nodes in the core network resulting in network disturbances for a limited number of customers in multiple countries,” the company said.
The group's chief executive Börje Ekholm also issued an apology in the late afternoon.
“The faulty software that has caused these issues is being decommissioned and we apologize not only to our customers but also to their customers,” Ekholm said.
“We work hard to ensure that our customers can limit the impact and restore their services as soon as possible.”