I wouldn't be concerned about site-to-site links (if we set any up) but would we be ok with calls across the Internet?aslong as you have QoS (Quality of Service) configured both on all switch gear and handsets aswell as gateways you should be ok
If we can get a 2Mb each way, 1:1, connection then I assume we can ensure QoS leaving our site but I don't know what happens after that - perhaps that depends on the destination and whether or not the PSTN network is used?
If we can get a dedicated line I would hope we can go for more than 2Mb.
There shouldn't be too much need for concern - what you're suggesting is that there is something fundamentally wrong with the core routing of the internet, which of course there isn't. As long as you can get a decent connection back to a datacentre in the London Docklands or similar area, the rest should take care of itself.