With MGCP controlled endpoints it is not necessary to configure the cptone command under the voice-port this is done automatically when the configuration is downloaded from CallManager.

Please refer to the following document link for adding a Cisco IOS MGCP Gateway, after step 9 it also details adding FXS or FXO ports to an MGCP gateway :-

http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/admin/6_0_1/ccmcfg/b06gtway.html#wp1311169

Hope this helps...

Rgds

Allan.

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