One of the reasons I selected a PCM interface adding a digital sound connection was because it allows me to connect sound to/from the MCU using I2S. As each GSM/GPRS Module also have both Ethernet & Wifi it is very easy to create a Mobile Home Phone Central with SIP Phones around the house. Using the fast backbone bus we can easily scale up to a quite large phone system. RS-X is a TDM protocol that is perfect for telecommunication, and bandwidth should in theory cover ca 60 voice channels on the backbone alone with 30-50ms algorithmic latency on the voice transport. Voice latency would actually be good because it is only static, algorithmic latency.
Keep in mind that this is 60 external lines only. Internal Ethernet/Wifi traffic will not be through the backbone. This design also have the advantage that we have an overkill in CPU power available in a truly distributed architecture.
This is a very interesting add-on capability to our Home Automation System.