Ferstl70,
Glad to know you managed to flash it with XP to use Arduino IDE.
According to other posts, if is flashed for Arduino then you loose the default phone app.
To reset everything to default you have to re flash it back to initial state, you can find this information somewhere (I think is on wiki) if not is on the forum posts. But then you loose the Arduino IDE programming capability.
There are some example to make calls under Arduino IDE in the example folder …
Enjoy!