freeswitch/conf/iax.conf.xml

<configuration name="iax.conf" description="IAX Configuration">
  <settings>
    <param name="debug" value="0"/>
    <!-- <param name="ip" value="1.2.3.4"/> -->
    <param name="port" value="4569"/>
    <param name="dialplan" value="XML"/>
    <param name="codec-prefs" value="PCMU@20i,PCMA,speex,L16"/>
    <param name="codec-master" value="us"/>
    <param name="codec-rates" value="8"/>
  </settings>
</configuration>