You can buy a SIM card for about 372.68 BDT, which includes 1 GB of data plan. You can choose from 5 telecoms: Airtel, Banglalink, Grameenphone, Robi or Teletalk.
Bangladesh uses GSM mobile networks GSM 900 and GSM 1800.
If you don't want to buy SIM card in Bangladesh upon arrival, make sure to check the roaming charges with your telecom provider before your departure so there are no surprises when you return home.