I only need it for bahn.de, but still...
install fmms
configure according to http://wiki.maemo.org/MMS_configurations#Germany
either
- send yourself an mms
- or send a sms with text 'ja mms' to 46667
Also helpful (in german): http://www.android-hilfe.de/tarife-provider-fuer-t-mobile-g2-touch/14251-mms-senden-empfangen-o2-geht-nicht.html#post152790