Downtime to the O2 network prevented the Prison Service from being able to monitor some criminals.
The network suffered around 24 hours of problems, resulting in some customers being unable to make calls, send texts, or access the web.
Security firm G4S uses O2 SIM cards in electronic tags attached to criminals and the Sun reports the outage may have rendered some of the tags untraceable.
Vans taking prisoners to court were also said to be affected and a spokesman for the Prison Service was quoted as saying the downtime caused "some minimal disruption".
"Contingency plans were activated. At no time was public safety compromised," the representative added.
The Daily Telegraph reports London's bicycle hire scheme was compromised, as the payment system relies on O2 technology.
Full services have now been restored and O2 has apologised for the loss of network.
It said in a statement the fault occurred in one if its "network systems" and has advised customers still having trouble to switch their phones off and on again.
Posted by Claire Marshall