Vodafone & Idea network integration is still on in New Delhi. If you face any problem then switching on data roaming plus restarting mobile is only solution. One may have to manually select Voda network if on Idea sim or Idea network if on voda sim. Here is the screenshot from one Idea Delhi user:
Vodafone Idea combined own largest spectrum in Indian mobile even then their network coverage is third in terms of reach and capacity. They are yet to launch Vowifi service. And are facing large churn from rival Jio n Airtel network.