Try this link.  It involved a Grandstream HT503 but it will work with your unit:

http://lists.freeswitch.org/pipermail/freeswitch-users/2011-January/067346.html

/Nandy

On Mon, Apr 21, 2014 at 11:34 PM, Mario G <mario_fs@mgtech.com> wrote:

Baffled for the last 2 days… I have an OBI110 connected to FreeSwitch as a user, so that it cal dial 911 out via a PSTN. Inbound is fine, but not matter what I do, it only dials out it’s own extension number (8181) on the PTSN line. I ran traces, etc. and don’t see what I am dialing, for example 3511, going to it. I tried to make it a gateway but FS returns 501 not supported. There are various web references to people using it for in/out on Asterisk and FreePBX but so put together FreeSwitch definitions in a similar way. I would really appreciate any suggestions at this point. I have tried many things, nothing seems to work. It always dials 8181 out. Thanks,

Mario G

<extension name="special.8181">

    <condition field="destination_number" expression="^3([23456789]11$)$">

        <!--action application="set" data="destination_number=**8$1"-->

        <action application="export" data="destination_number=$1"/-->

        <!--action application="bridge" data="user/8181@${domain_name}"/>

        <!--action application="transfer" data="8181"/-->

        <action application="bridge" data="sofia/internal/$1%${sip_profile}">

    </condition>

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_________________________________________________________________________
Professional FreeSWITCH Consulting Services:
consulting@freeswitch.org
http://www.freeswitchsolutions.com

FreeSWITCH-powered IP PBX: The CudaTel Communication Server
http://www.cudatel.com

Official FreeSWITCH Sites
http://www.freeswitch.org
http://wiki.freeswitch.org
http://www.cluecon.com

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