We've got it set up okay here Iain. We just use OWA details to setup email on each phone / tablet so don't need POP3 or IMAP, or set up any extra ISA rules. Balckberrys don't work as we havn't got Enterprise Manager but managed iPhones, iPads, Android and Nokia so far.
Here's an example iphone setup,
Server: OWA web address
Domain: Local Domain
Username: Username
Password: Password
Use SSL: On
Let me know if you need more info, good luck.