How do I get a SIM card in Bahrain and which is cheapest for calling Bangladesh?

Bahrain's main operators are Batelco, stc Bahrain and Zain. Buy a prepaid SIM in person with your passport, which is required to register (fingerprint plus passport at the point of sale). The cheapest starter is around BHD 4 (Batelco), with Zain and stc a little higher. For calling Bangladesh, compare the international minute bundles, or use app-based calling over data, which is usually cheapest. Zain's prepaid, for example, offers weekly and monthly bundles with call minutes and data. Once you have your CPR card you can switch to a postpaid plan. Keep the SIM registered in your own name so you keep control of the number. There is a limit on new numbers per CPR per month.