NotifySync works great. I have it running on a Blackberry Storm and a Blackberry Bold with no issues. The best part of Notifysync is since it uses the standard TCP network of the wireless carrier, there is no reason to have to purchase the BES plan from your wireless carrier. Saving you $15 a month per phone. I would really recommend it to anyone that uses a Blackberry and Zimbra. Another final note, its endorsed by RIM, so you will get support when you call if you have a phone issue. Here is the link.
Research In Motion