With my 3G data plan, I like to chat if I have time. Right now, I am still using Agile Messenger, a shareware multi protocol instant messenger. But if you only plan to use MSN, you can use Hier.
Hier is an instant messaging client for MSN protocol. This program is quite easy to use, and supports most MSN functionalities (including sending and receiving attachments). One thing that I don’t like is that the font display is sometime cropped.
This program can be downloaded from: http://hier.ppsay.cn/EN/