I guess you are looking for a SIP Proxy acting as SBC. This could be OpenSIPS forwarding REGISTER attempt to REGISTRAR server while INVITEs are handled by FS !
I don't think FreeSwitch can't handle forwarding of Registrations (is not a SIP proxy)

On Fri, Sep 16, 2011 at 1:56 AM, envelopes envelopes <sunwood360@gmail.com> wrote:

Most of them are cases where FS access external as gateways.  What I am looking for is usage case that extensions are registered to 3rd party registrar, and FS is integrated with the registrar.

On Sep 10, 2011 5:28 PM, "Gabriel Gunderson" <gabe@gundy.org> wrote:
> On Fri, Sep 9, 2011 at 3:19 PM, envelopes envelopes
> <sunwood360@gmail.com> wrote:
>> Is there any config examples of freeswitch working with external registar?
>
> Try this:
>
> http://wiki.freeswitch.org/wiki/SIP_Provider_Examples
>
> Gabe
>
>
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