You can easily buy a new ooredoo or Vodafone SIM on arrival at Doha International Airport
Once you have made it through customs it may be a good idea to buy a local SIM for use during your stay in Qatar. Qatar enjoys absolutely excellent mobile coms, with fast and reliable mobile data. You will need your passport for ID when buying a SIM in Qatar, and they will take a copy of your passport and register it against your SIM.
to buy a new SIM. And both have very similar pricing for data and calls. It would take a great deal of comparison to try and decide which one to go for on price alone. And I would not want to be sued by either of them by saying one had a better network than the other. So the choice is yours. But ask them both about their Fexi plans because I believe they represent the best value for visitors.
For Vodafone once you have walked to your left you will quickly come across a WH Smiths store. This is where you can buy your Vodafone SIM.
If you walk out of customs and turn right, you need to walk to the end of the building (follow signs for buses) and you will see a big ooredoo stand by the escalators.
Take you new SIM, pop it into your phone and you are good to go.