Up to 200 customers' phone lines went dead when thieves stole 400m (437 yds) of copper cable in Staffordshire.
The thieves broke into a telephone control box at Mitre crossroads, on the A515 near Newborough, on Tuesday.
Officers were informed after people in the area noticed their phones had stopped working and a BT engineer was sent to investigate.
Staffordshire Police have appealed for anyone who saw anything suspicious in the area on Tuesday to contact them.
A BT spokeswoman said two cables serving up to 200 customers were stolen and engineers were working to repair faults affecting about 30 phone lines.
She said temporary traffic lights had been erected while work was carried out, as the section road was an accident black spot.
She said the firm hoped to restore customer phone lines before the end of Thursday.