"you can never win an argument against a M _ _ _ N"
Anyway, Dude your phone will indeed get a bit choppy because you will have to consider 2 different classes of QoS. That would be Conversational Class and Streaming Class. You can ask your provider about g.729 codec since it requires low bandwidth, but I think you have to add a few bucks for its license. However, this will clear your internet pipe a bit for the traversal steaming bandwidth. My maximum concurrent users on a single Asterisk Server (512kbps hosted in colo facility) is 25 users, this is without video of course. I think 2mbps is more than enough though if you properly configure your router's QoS settings. On the provider, I would suggest pldt business plan (Because of the higher CIR - would cost you just 4k+ a month I think).