Bring the i2004 to the site where the BCM resides. Connect the i2004 to the same LAN as the BCM and make sure that the phone upgrades the firmware and operates fine. Once you are certain that the phone is operating correctly on the LAN, take the i2004 to the remote site and try again. If you're still having issues, it's a firewall or VPN problem (depending on how you're connecting).
Good luck.