Is Blackberry Compatible with Exchange Server 2007?

I recently upgraded to Exchange Server 2007. Since then none of my corporate emails accounts are able to validate with the Blackberry 8700g. I have tried editting and deleting the account and it wont sync with my email server. I have ended up using the Blackberry redirector to get emails to my blackberry but most of my users work from laptops so having them leave their laptops at work and locked just to receive emails on their blackberry’s. Is there a fix for this problem or am I left with buying the Blackberry Enterprise Server?