Status Report from today:
As I read in this thread in the mornig, somebody suggested to switch the regional setting to Germany I did so:
Everthing worked fine the whole day, I can use the number pad, use Messages, Caller lists. Had not one Problem today. Just now I did a sync at home, still everthing fine.
By the way: Edge is working w my A1 SIM, even before.
So for me the problem has now a acceptable workaround, for sure I am expecting a fix also for the austrian regional setting.
Also I was in Passau today and bought the BT Headset: cool. I asked the lady there, if they heard from problems w other than German Simcards, but they don't, even they have sold some iPhones to austrians. Somewhere else in the forum I read, the iPhone has to be connected first w a german t-Mobile card to itunes, after that reset the network settings and someone can use other Simcards. This seems not to be true, they just call a hotline and report the IMEI.
So, best regards to everybody
Christian