I finally got it working that I can use a Huawei E173 modem on my raspberry. When activating it with
sudo ifup 3gModem
everything works fine, and it connects itself to my Server as I can see it in the log files. But when I try to connect to the modem IP via port 22 it won't work. Same with apache. I installed an apache server on it. And when i call the raspberrys IP over the wlan0 interface I can access is, with the ppp0 interface it completly blocks everything that goes into the pi. Not even pinging is possible. Do you know any solutions to this? I tried googling for sometime but nothing useful came up