Voipms support more than g729.
allow=g729; we support alaw,ulaw,ilbc,gsm,g723.1,g726,g729a
But anyway let’s say you want to use g729 and you have a one channel license, the problem is with your xlite configuration. Your g729 license will server as translation between the codec you will use in X-lite and your iax connection with voipms. X-lite doesn’t support g729. I recommend iLBC for x-lite if you need a low bandwidth codec, otherwise g711.u or g711.a (ulaw/alaw) if you have good bandwidth. But it would be a waste of bandwidth since you connect your iax channel with voipms in g729. If you don’t want translation and low bandwidth codec, why don’t you use iLBC or GSM on both your IAX provider and your X-lite config.
So your x-lite config should be as follow:
callerid=“Toure Mamadou” <5678>
host=dynamic ; This device needs to register
nat=yes ; X-Lite is behind a NAT router
canreinvite=no ; Typically set to NO if behind NAT
Then in x-lite, you go to right click on it, click options, click “advanced” at the bottom of the left menu. Click on Audio Codecs, and make sure you put the codec you want to use on the right of the allowed codecs and remove the ones you don’t want.