asterisk users - Dec 2004 - setting up asterisk as voicemail for softswitch

Im trying to get my asterisk box to register to a sip provider without much 
success.

here is my console output in asterisk
Dec 13 12:57:17 NOTICE[213005]: chan_sip.c:3982 sip_reg_timeout: Registration 
for 'voicemail.nexband.com@metaswitch.nexband.com' timed out, trying
again
    -- Got SIP response 403 "From: URI not recognized" back from
208.149.73.5
Urgent handler

in my sip.conf i have
register => voicemail.nexband.com@metaswitch.nexband.com

i have authentication turned off on the softswitch and the sip username is 
voicemail (sip domain name is nexband.com).  using tcp transport to port 
5060.  no firewall in place between the two.

sip show registry
Host                            Username       Refresh State
metaswitch.nexband.com:5060     voicemail.ne       120 Request Sent

i tried voicemail@metaswitch.nexband.com & 
voicemail.nexband.com@metaswitch.nexband.com with the same results

any suggestions?
-- 
Chad Whitten
Network Administrator
neXband Communications
cwhitten@nexband.com
601-944-4801 Phone
601-944-4803 Fax