Is there a possibility to simulate throttle the download to the speed of GPRS, 3G and so on (cellular connection) while I am connected with an Ipod Touch (IOS 4.2/4 Generation) to the wifi?
What I want is to get a feeling of the duration when I am loading e.g. some images or xml files from a server.
It's not exactly what you're after, but you can do this on your Mac and test in the simulator.
Open the terminal and enter:
sudo ipfw pipe 1 config bw 15KByte/s
sudo ipfw add 1 pipe 1 src-port 80
This throttles your connection to 15KB/s - which is approximately 3G.
Testing in the simulator will now be like using 3G.
To put your connection back to normal, you can enter:
sudo ipfw delete 1