If all you did was upgrade the IOS. And reverting to the previous IOS gives you full duplex communication. In my opinion you are running into a software bug. Please open a TAC case so that this can be troubleshoot and the appropriate information rout...

Current Cisco end-point implementations do not take into consideration Mobile IP (they are not aware of the existence of a Home Address and a Care-of-address that will change as the node moves). Symbol has been working on wireless mobile clients for ...

please check your partitions and calling search space. If the new phones are not in the correct calling search space, they may not be able to reach the partition where Route Pattern associated to the gateway resides

This release definitely supports SRST and as for MOH, it is also supported, with the exception of multicast MOH streams. So you should be in good shape if you're using unicast streams.

You may want to open a TAC case and provide access to the engineer. They can run these checks in a little while. Probably more time effective for both parties.