I am in Austria for a couple of days again and finally had the chance to get hold of a 3 Prepaid SIM card for Internet access. The price 3 charges per megabyte is 80 cents. It’s a bit too expensive to be used with a notebook but o.k. to check eMails and surf the web via the mobile phone.
The SIM card is €19,90 with an already included balance of 5 euros. When buying the SIM card make sure packet data services are activated for the SIM card in the shop. The access point name (APN) for web, eMail (POP3, SMTP), etc. is "drei.at". For easy access and bookmarking I’ve put the information on the Prepaid SIM Internet Access Wiki as well.
P.S.: For Internet access with a notebook while roaming in Austria, Vodafone Germany’s Websession offer is still the best choice.