This is a big misconception. I have experience with Asterisk and the Mizu VoIP softswitch only. Asterisk is quite limited on capacity, but that mizu server can

This is a big misconception. I have experience with Asterisk and the Mizu VoIP softswitch only. Asterisk is quite limited on capacity, but that mizu server can handle 10000 simultaneous calls on a cheap Xeon server (full B2B calls with billing and RTP proxy and all the PBX stuff such as IVR, voicemail, conference). This capacity is enough for a whole smaller country and these kind of software solutions can be easily scaled. Of course, you can buy the same capacity 100x more expensive from a hardware vendor.