A group of us went to buy Austrian pay as you go cell phones since we had decided not to pay for international services. After asking around we found out that the T-Mobile pay as you go phones were the best idea if you were planning on traveling as they would work internationally, other options were A1 and Telecom, but they sometimes were less reliable internationally. Just a heads up that in Austria a cell phone is called a Handy.
Our group went to the miniature mall that is at the Salzburg Hauptbanhof (main train station). You can take pretty much any bus to the Hauptbanhof but bus 4 (if it is still the same route schedule) is the main bus to take. Once we got the the mall we found the T-Mobile store and got our cell phones easily as the people there spoke very good English. Make sure you bring your passport with you otherwise you cannot get a phone. Ask them to set it up for you because otherwise it might be confusing to validate your phone. We were surprised at how much the phones cost. Just for a pay as you go phone it was about 30 euros and then you had to add on phone credit!
Be sure to keep the little plastic card that the SIM card comes in with you because it has your PIN number on it. Unless you are great at memorizing it is good to have around because you have to have it to get into your phone if you turn it off or it falls and you have to restart it.
To get more phone credit without having to go to the Hauptbanhof, you can go to any Austria Tabak or Tabak Traffik on the streets and ask the cashier for some Handy Credit. They will ask what provider and make sure you say for the company you have, for example T-Mobile. You can only buy it increments, and you will get a receipt that has a directions and a code on it to put into your phone to gain the credit.