Up to 35,000 people in Birmingham are unable to use their phones or contact emergency services after thieves damaged cables during a burglary.
BT engineers have managed to restore 3,000 lines but say it may be Monday evening before all are restored.
The 999 service in much of Birmingham and the Black Country is unavailable. People are asked to use mobile phones.
A police spokeswoman said raiders cut through BT cables at an exchange near Handsworth Sorting Office.
The raid happened in the early hours of Sunday.
Anyone in need of the emergency services is advised to contact the police switchboard on 0845 113 5000 and state the call is an emergency.
The fire service can be called from the red phone boxes outside fire stations. People should also raise the alarm with neighbours, shops and passers-by.
The affected areas include Aston, central Birmingham, Perry Barr, Handsworth, Ladywood, Blackheath, Stone Croft, West Bromwich, Tipton and Wednesbury.
There is a complete service loss in some areas and a partial loss in others. It is also affecting normal phone services.