If you lost your Handset of something happen in your SIM card and need to get another new SIM card.
It's not very easy if you don't have Subscription paper. sometimes they just ask few question and you get it. if it happen postpaid or some kind of official then it's better to go your next door who know you. s/he can help you without any kind of paper or sign complex.
Usually following the system of GrameenPhone SIM Replacement System.
Contact Point: GPC, Retailer outlet, Service Touch Point
For individual subscription - Subscription paper will be required
For corporate subscription - To replace or change SIM card key contact person needs to send an application in letterhead pad / fill up SIM replacement form with proper company seal and valid sign & come to any GPC/GPSD/GPCF.
For some special organization (Bangladesh Army, Navy, Air Force, Rifles, Police, RAB, Ansar & VDP, Special Security Forces, President Guard Regiment etc) - SIM card can be replaced or changed with the signature & seal of the respective unit heads or certain high ranking officers rather than key contact person.