Hi Andrew;
I guess you can do it by using jxme. I tried chat demo application before and it is just fine.
By using JXME, any MIDP device can join peers with other MIDP clients. On the other hand you can also connect some peers available,lets say PCs/servers..etc with some restrictions.
To learn more visit
http://www.jxta.org I hope this will help you,
Cheers;