Try these settings:
WAP GPRS:
APN: wap.eplus.de
WAP-Gateway: 212.23.97.9
Startseite
http://wap.eplus.de
Sicherheit: aus
Benutzername: Eplus
Passwort: wap
Internet GPRS:
APN: internet.eplus.de
Benutzername: eplus
Passwort: internet
As far as I remember, user name and password are optional, but maybe this is not correct and the wrong password might cause the problem.