Thank you for testing Rich.
One problem with using IMAP/SMTP is that it's not allowed with every "data plans" by some carriers : at least here in France/Europe, carriers either "http only" data plans or "full" data plans.
If you have a "http data plan", you can not use IMAP/SMTP while you can use ActiveSync for Exchange.
I've found
this: on a Exchange 2003 setup, the Outlook Mobile charset can be set serverside.