SIM cards purchase in Austria

[otani]

Hi all,

I'm visiting Graz, Austria in June and July for 10 days, and looking
for a good prepaid SIM card for me and my group members. We all have
unlocked cell phones, so all we need is local SIM cards. I've found A1's
B-Free 5, T-Mobile's Klax Club and Orange's Orange Wertkarte attractive.

My questions are:
1) Are all those SIM card easily available at the Graz/Vienna airport? If not, where can I get them, including recharge?
2) If I bought T-Mobile's Klax Start, how do I switch to Klax Club?
Is that easy and with no extra payment involved?
3)Are there any general suggestions for short-term visitors using cell
phones in Austria?

Sincerely,
Hiroshi