Right now my gripes with cloud telephony are not only the lack of transparency which you cover quite well, but also vendor lock in. What happens when your provider goes under, doesn't have it together technically, or decides to raise prices, changes use policy, etc, ad infinitum.<p>One of the great things about open source telephony (like Asterisk) is how you can actually use multiple service providers at once. If one fails you can drop over to the other, or even use the cheapest one for the call context. It's a nice efficient marketplace.