If you own a unlocked iphone maybe you want to use the carrier e-plus in germany. You just have to adjust the settings for mobile network as shown below:

choose settings – general -network – cellular data network and set the following parameters:

APN: internet.eplus.de
Username: eplus
Password: internet

You can set here your mms settings, too:

APN: mms.eplus.de
Username: mms
Password: eplus
MSSC: http://mms/eplus
MMS Proxy: 212.023.097.153:5080