eMSN is a free Java J2ME based software for mobile phones. This is the only software for mobiles that I am aware of that claims to work with a WAP based internet connection.

Features:
MSN instant messaging
Add/remove contacts
Invite contacts
Emoticons (extra emocticons in version 6.0.12)
Snap and send photos during a chat. The other users in the chat room will receive a link where they can watch the photo. Sending photos via eMSN is much cheaper than MMS and can recive both mobiles as PCs.
Personalize your photos using Snap&Sketch
Receive photos from other eMSN mobiles
Send emails
Easier navigation since version 6.0.12

There are two different versions, one for MIDP 1 i.e. eMSNLite and one for MIDP 2 devices- eMSN