I have some IX-5900 and 5910 phones that I am adding to an ECS running 8.0 (though it was upgraded from 2.1 to 8.0 prior to the MBU being installed in the system) that can make calls to IP handsets without any issue, but calls to digital handsets (or through the trunk lines) have no audio.

I've ensured that the MBU is programmed correctly in the ECS for the slot and MAC (as well as swapped in a known good MBU), as well as making sure that the MBU is updated to the latest version (1.22).

If I connect the phone directly to the MBU everything works great (I can make calls to/from TDM resources on the IP phone), but if I move the phones to the network the audio stops working.

The site in question is using Cisco switches throughout. They *do* have VLANs set up, but all of the ports are configured in the switch to be tagged with the proper VLAN. There aren't any protocols or ports blocked on the network.

Is there anything in particular that I should be looking for on the network side of things that can be causing this behavior?