Dear Priya,
This is a very nice topic. Let me tell you tht there is nothing which has only positive or negative effects. Hence, what is needed is understanding the thing and then making a decision. Everyone knows that coke or pepsi is harmful for health, yet people drink it. As others have said, the main reason for joining call centres is that even though people are not very qualified, yet it is very easy to get a job with a high pay package and good growth rate, yet, this comes at the cost of a major health issue. Hence, it is necessary to understand its sides before jumping in for it.
No one can't really say with affirmity whether its a boon or bane. It all depends on what is your definition for boon/bane.