Mitel released the following artical today:
Mitel has implemented the G722.1 CODEC using a 32Kbit bitrate. This means that in order for any third party device/application to work with MCD 5.0 they must support this bitrate. If a device/application attempts to use G722.1 with a different bitrate, you will encounter a no audio scenario.
If you do come across this issue with an incompatible version of G722.1 then a few options exist depending on the integration medium used.
Option 1: Disable the G722.1 CODEC globally on the 3300 using the maintenance command addcodecfiler (Please see 3300 help on the proper syntax to use.) However, this means that the CODEC cannot be used by any device (including IP sets) connected to the 3300.
Option 2: If the third party device/application is connected to us via SIP trunks, you may set "Renegotiate SDP To Enforce Symmetric Codec" to Yes in the SIP Peer Profile of the device/application in question. This will ensure you don't run into any audio issues and this also doesn't require you to disable G722.1 globally as you would with Option 1.
Option 3: If the third party device/application is connected to us as a SIP phone, you may set the same option as in Option 2 but this time in the Sip Device Capabilities form for the specific device that is not using a compatible version of G722.1.