said by UHF:
I'm not sure of what CallCentric is using for a switch, but from what they've said in the past, it's carrier grade telecom switches (most likely Lucent), connected to an SS7 and most likely TDM network. That's not any more "proprietary" than an Asterisk server. More expensive to make redundant - definitely, I can't argue that point. Which one is better? When all hell breaks loose probably the Asterisk box!
They're also doing their own switching and interconnecting with actual telecommunications networks. Whereas, these Asterix box providers are basically reselling services and using trunks wholesaled from other providers and are essentially tier 3 voip providers.