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

The two networks are Ooredoo and Vodafone. You need your passport or QID to buy a prepaid SIM. Buy from an Ooredoo or Vodafone shop, the airport, or a supermarket like Lulu or Carrefour. Ooredoo prepaid is called Hala; a Hala Super 35 costs QAR 35 for 30 days with local and some international minutes. Vodafone international add-ons start at QAR 10 for about 18 minutes to Bangladesh. To call Bangladesh cheaply, add the Bangladesh international pack. Prices change often, so check the shop or app for the current pack.