After browsing some documentation, I figured out how to use an iPhone / iPod touch as VPN client in our university network. This saves you a lot of time as you don't need to enter login information at the WLAN gateway.
(German text below!)
Use the following settings at Settings > General > Network > VPN > Add VPN Configuration > IPSec:
Description: Uni Ulm
Server: vpn.uni-ulm.de
Account: <KIZ Account>
Password: <KIZ Password>
Use certificate: not active
Group Name: UU-All-Hybrid[hybrid]
Secret: tiavip