Taken from Microsoft KB2664650
Microsoft push notification messages are not delivered to Lync mobile IOS and WP7 clients, when URL filtering is configured on Lync 2010 Edge Servers or office communication 2007 R2 Access Edge Server, apparently this is caused by:
with the release of the new Lync 2010 mobility service, Microsoft also has released what is called push notification service, many administrators like myself were surprised about this after reading Microsoft official Mobility guide and I bet many of them still doesn’t have a clear idea about how the push notification service works, and if is it required to be configured or not.
what is this Service used for ?
The Service is a cloud-based service located in the Lync online Data Center, it is used to send notifications to Lync mobile clients running on windows phone 7 and IOS based systems.
The push notification Service push notifications to mobile clients n the form of badges, icons, or alerts, even if the mobile application was inactive. Push notifications notify a user of events such as a new or missed IM invitation, missed calls, and voice mail.