Hi Shiani,
This is the list of some call centres in Mumbai. I got this list from this site only.
Amex Information Technologies
Connectvantage Solutions
e-funds international
e-serve international
Global eCMS
Infowavz
Transworks Information Services
Zenta Technologies
spectramind
sitel
Tata Infotech
Global Tele Ltd
Hinduja Tele ltd
Bharati Airtel