The main reason I chose such a setup instead of centralized, is because Sonos makes it own mesh network by letting all the zones 'talk' to each other.
That's my favorite thing about Sonos. It's pretty simple.
You'll need something with IP control or an external IP controller in the mix.
URC's product has IP control/messaging (2-way). The key is then finding software on the smartphone/tablet of choice to control it. There should be something available as I think there are expandable solutions that support the IP-based products of most vendors.
Example app:
http://www.roomieremote.com/ip-compatibility/Bruno, I must have missed the part about multiple sources. I don't think that's an issue. I think he's mostly just interested in playing music in multiple rooms from a smartphone, but I'll certainly bring it up and see if he's interested in that...