The best bet would be to try NetFront 3.1 with Java Lite, but I'm not sure if this will work. You may want to log into Yahoo!'s Mobile site @
http://wap.oa.yahoo.com
I can't remember if they have a mobile chat link in there or not.
I doubt turning on scripting within PIE would allow you to use the main chat app, as it relies on either the MS Virtual Machine or the Sun Java client. There are several utilities which you can use to enable scripting in PIE.