when add a new trunk,it can register to the provider,but when call out ,I receive "404 not found"

I have captured and find out that the "To" message is different,
For trixbox,it sends message this way:
To:
SIP to address: sip:019918858199@211.29.10.45
but a IPphone send like this way:
To: 019918858199
SIP to address: sip:019918858199@211.29.10.45
How can trixbox send "To" message like the ipphone sends.