i have 2 FS server connected, FS A reg to FS B, and FS B is a gateway for FS A, the external conf of FS A is 

<gateway name="gwB">

<param name="username" value="1000"/>

<param name="password" value="1234"/>

<param name="realm" value="192.168.0.100"/>

<param name="proxy" value="192.168.0.100"/>

</gateway>

and i can make call from a phone(e.g. 1001) regestring in FS A to one(e.g. 1005) in FS B, but the calling number shown on the called party is "1000", how can i pass the original caller number("1001") to the called party in FS B?