"The network faced some technical problems in Noida, services were been badly affected in Delhi and NCR areas, and our team is on work to rectify the problem. It will take some more hours to resolve the fault," Idea's friend desk executive Gurvir Singh told IANS.
The network failed around 10.30am IST.
Despite several attempts, company officials were unavailable for any further details.
When customers tried to make a call earlier in the day, a "Mobile network not available" message appeared on their screens.
"I thought it was some problem with my mobile set and I came to know about the network failure after I went to one of the idea customer care centre," said Ravinder Yadav, an executive with a private firm.
Confused subscribers queued up in front of several customer care centres, failing to understand whether their handsets have developed any problem or the service provider has withdrawn their connections without intimating them.
Late in the evening, a communication officials said: "There is no update on this matter."