Source page
https://www.facebook.com/mtnlmumbai/photos/a.198197806911697.52509.197750196956458/908180095913461/

1. Now MTNL landline customers can call any landline or Mobile number both in Mumbai as well as Delhi absolutely FREE,
2. Apart from this the STD calls made through landline will be charged @ 180 secs per unit during the same period.
3. These rates will be effective from 1st May 2015.
4. These facilities are not applicable to ISDN BRA, PRA, All types of PCO’s , DID/ DOD Fra
5. nchisees, Level 1, IN services and for all special customized plans. Hurry! Book your MTNL landline now. #Unlimitedfree