Which sim card will be cheaper to call India daily, for one week, from Beijing?

Jagdeep, you'd better figure out what mode your phone supports, WCDMA, GSM or both? If so, you should choose China Mobile or China Unicom. If you make direct calls, then the fee is the same no matter you use any of the above mentioned carrier. However, China Mobile has international call packages. If you subscribe the package, then the cost is cheaper.