When the phone first registers, the sbc replies with a 404 not found. The phone will send another register and then it passes thru the upper registration and then registers to my switch.

Is this expected behavior, and is there any way to prevent the sbc from sending the 404 on the initial invite?
I would think when it encounters a "UNREGISTER FOR A **NON-EXISTING** SESSION" it should go ahead and create a new session instead of sending the 404.

2009/09/30 07:57:58.519 INF: [CID=0xcb140f65] <<< REGISTER sip:sbc.mydomain.com:5060 SIP/2.0 Method(REGISTER) SRC: 64.82.228.20:5060:UDP enc=0 bytes=563
2009/09/30 07:57:58.525 INF: [CID=0xcb140f65] *** UPPER REG *** sip:sip1112221234 at sbc dot mydomain dot com:5060
2009/09/30 07:57:58.525 WRN: [CID=0x4e67c6a7] GOT UNREGISTER FOR A **NON-EXISTING** SESSION
2009/09/30 07:57:58.525 DTL: [CID=0xcb140f65] NIST(1254315478520) Event(SIPMessage) - SIP/2.0 404 Not Found
2009/09/30 07:57:58.526 INF: [CID=0xcb140f65] >>> SIP/2.0 404 Not Found Method(REGISTER) DST: 10.100.0.20:5060:UDP SRC: 10.0.0.100:5060 enc=0 bytes=355

2009/09/30 07:58:01.551 INF: [CID=0xcb140f65] <<< REGISTER sip:sbc.mydomain.com:5060 SIP/2.0 Method(REGISTER) SRC: 10.100.0.20:5060:UDP enc=0 bytes=554
2009/09/30 07:58:01.552 INF: [CID=0xcb140f65] *** UPPER REG *** sip:sip1112221234 at sbc dot mydomain dot com:5060
2009/09/30 07:58:01.552 DTL: [CID=0x4e67c6a7] *** REG *** Session CREATED. AOR=sip:sip1112221234 at sbc dot mydomain dot com:5060
2009/09/30 07:58:01.552 DTL: [CID=0xcb140f65] UPPER REG: New request being processed
2009/09/30 07:58:01.552 DTL: [CID=0xcb140f65] UPPER REG: Received Registration Request
2009/09/30 07:58:01.553 DTL: [CID=0xcb140f65] *** REG *** Record CREATED. AOR=sip:sip1112221234 at sbc dot mydomain dot com:5060 Binding=sip:sip1112221234@192.168.69.238:5060
2009/09/30 07:58:01.556 INF: [CID=0xcb140f65] >>> REGISTER sip:sip1112221234 at switch dot mydomain dot com:5060 SIP/2.0 Method(REGISTER) DST: 10.0.0.200:5060:UDP SRC: 10.0.0.100:5060 enc=0 bytes=788