Ofcom investigates BT and Three after mobile call outages

Ofcom has opened formal investigations into BT and Three following major mobile network outages earlier this year that disrupted call services across the UK.

Both incidents affected customers' ability to make voice calls, including calls to emergency services.

The regulator will assess whether the companies complied with legal duties around network resilience and outage reporting.

Source: Ofcom

BT and Three outages trigger Ofcom probe

Ofcom has launched investigations following two separate mobile network incidents reported in summer 2025.

BT notified Ofcom of a software issue on 24 and 25 July that caused a UK-wide disruption to mobile calls on the EE network. The issue affected call connectivity between networks and prevented some customers from making or receiving calls, including emergency calls.

Three separately reported a nationwide outage on 25 June that disrupted its mobile call services. The incident also affected customers' ability to contact emergency services.

Under UK telecoms rules, mobile networks are required to plan for failures, reduce the risk of disruption and respond quickly when outages occur. These expectations are set out in law and backed by Ofcom guidance on network resilience and outage reporting.

Ofcom said its investigations will seek to establish the facts surrounding these incidents and assess whether there are reasonable grounds to believe that BT and Three have failed to comply with their regulatory obligations.

When mobile calls went dark

The outages affected millions of mobile customers on the EE and Three networks across the UK.

During both incidents, customers took to provider forums and outage trackers to describe similar problems with basic voice services, including:

• Unable to make or receive calls, even with signal showing
• Calls failing to connect or cutting off immediately
• Loss of voice service across large areas
• Uncertainty over when calling would be restored

Reports from Three customers during the 25 June outage focused on a widespread loss of calling, while EE customers affected by the July incident described problems making calls to numbers on other mobile networks.

In both cases, the disruption affected voice calling rather than mobile data services and included problems contacting emergency services.

Ofcom said customer impact will be a key part of its assessment of whether the companies met their obligations to maintain network availability and protect access to emergency calls.

Wider test of mobile network resilience

Ofcom's investigations come amid growing regulatory focus on the resilience of UK telecoms networks, particularly where outages affect access to emergency services.

The regulator's Network and Service Resilience Guidance says providers are expected to design networks to reduce risk, identify potential points of failure and mitigate the impact of incidents when they happen.

In that guidance, Ofcom also makes clear that compliance is not limited to preventing outages. It includes effective planning, monitoring and response when failures occur.

Those expectations align with wider efforts to protect vulnerable users during major infrastructure change. Telecoms firms have committed to stronger safeguards for people using safety alarms as part of the UK's move away from traditional landlines, including clearer identification of vulnerable customers and additional support where services are safety-critical.

As the digital landline switchover progresses, telecare users and their families are also being urged to contact their landline provider in advance to check how alarms and emergency services will work after the change, and whether additional equipment or support is needed.

Mobile networks are therefore increasingly treated as critical infrastructure, not just for everyday communication but for public safety as traditional landlines are withdrawn.

That growing reliance raises the stakes for basic voice services. If Ofcom finds that BT or Three breached their regulatory obligations, it has the power to impose penalties or require changes that could shape future expectations around network resilience and emergency-call protection.