A SIM card bought in Austria will also work in Germany and Hungary, though you will be roaming, so the charges will be slightly higher. Not sure about buying a SIM at the Salzburg airport, since I haven't been there in years (before cellphones). A locally purchased SIM will be a lot cheaper per-minute than a Eurobuzz SIM. I keep a Eurobuzz SIM in my dual SIM phone as a backup, but in the other slot I keep a local SIM. On my most recent trip to Spain, Eurobuzz was charging something like 79 cents a minute. The local SIM I bought was less than 20 cents a minute. The benefit to a Eurobuzz SIM (and the main reason I keep it) is that your number is permanent - it never expires - and you are charged after the fact instead of buying minutes upfront. In case of an emergency, my family can always reach me on my Eurobuzz number, even though my local SIM numbers change.