There are major domestic and international BPOs' in India. The basic qualification required by an international BPO is any bachelor's degree. But many accept class 12 pass as well. Domestic BPOs' easily accept an undergraduate/12th pass.
Apart from these qualifications, international call centers want applicants to have a neutral voice accent. So that with training their voice can be modulated to country-specific requirements. Whereas domestic call centers want people well-versed with the state's regional language viz. Marathi, Tamil, Malayalam etc.
So it all boils down to having basic graduation/undergraduation with good communication skills.