It's not easy to figure out how to connect to the NUS wireless network through PEAP.
Here are two solutions for the problem:
The first one is by NG, Jun Ping(http://www.comp.nus.edu.sg/~junping/NUS-iPhone-Wifi.htm)
There is a configure file need to download: NUS-Wireless.mobileconfig
Then open the file with a text editor and look for "nusstu\xxxxxxx". Replace it with your NUSNET ID.
Now try to transfer this file to your iphone using ftp,bluetooth or email(as suggest by the author).
Open the file and install the configuration NUS-Wireless.
Then switch the wifi to NUS, and type your password when you are asked to.
At last you should accept a certification, and you now can connect to NUS.
The second solution is provided by Lester Chan
The two solutions are in fact the same. Lester Chan' method would be simpler, that the configuration file is automatically generated, but you need to provide your NUSNET ID to 3rd part server.