Regading iPad & iPhone push
Your iPad may be WiFi only (or 3G with service deactivated). If so, your WiFi may connect/disconnect periodically severing the open request for push notifications.
If you do have 3G on as a fail over connection when WiFi is not available, then make sure your exchange server's IP address is the same over 3G as it is over WiFi. If your office WiFi is internal, it may be possible you have an internal DNS as well issuing an internal IP address for your exchange server.
When your iPad moves from WiFi to 3G and back, the push connection is severed because of this change of IP and consquently push may be affected. If both WiFi & 3G report the same public IP for your exchange server then you should be good with continuous push.