Here's a service that was brought up here in PPC Geeks land about a week or so ago that gives you OWA 2007 and Push Email.
http://win.alol.net.br/simple/
I signed up just to check it out and it works as advertised...although it's in Brazil...
Get a FREE push email for mobile from alol.net.br
You’ll never be far from your emails, contacts, schedules and other information again! More than just an email solution, it’s a complete messaging, calendaring and task management.
Free Direct Push Email Yes
Mobile Device Synchronization with ActiveSync Yes
Outlook Web Access client Yes
Storage 1GB
Attachment Size 100MB
Calendar, Contacts, Tasks, Reminders, Journal Yes
BlackBerry Mobile Add-On Available Yes
Microsoft Windows Mobile Device Supported Yes
RoadSync Add-On Supported Yes
Import your existing Contacts Yes
POP3, IMAP and SMTP Support Yes
Cost: FREE