Thanks Folks; I'm making progress. The following origination string does make my non-registered SJPhone ring:
{origination_caller_id_number=2000}sofia/external/some@192.168.50.67
But why isn't it caught by the following extension?
<include>
<extension name="myextension">
<condition field="caller_id_number" expression="^2000$" break="on-true">
<action application="socket" data="192.168.50.67:10000 full" />
</condition>
</extension>
</include>