I don't know what your settings are or what you're trying to accomplish. If you're trying to "add a field" to the native SIP app in the 900, that's way above my pay grade. If you want to run your SIP service through a PBX trunk, it may add some extra functionality to your SIP service, that the 900's SIP client can not provide. Check out the instructions here for setting up a trunk on pbxes.org: http://seethisnowreadthis.com/2009/0...android-phone/ ...just ignore the "Android" part. The instructions are mainly for setting up the trunk on pbxes. Then log in to the pbxes account on the 900 with pbxes credentials, after creating an account with them.