A new scalable VoIP solution
Ubiquity Software seems to be making a splash with a new SIP package described in the link excerpted here,
Ubiquity Software, which provides SIP application solutions for communication services, debuted its Ubiquity Voice Plus, a cost effective, scalable solution for consumer IP telephony and multimedia services. Building on Ubiquity’s early success in consumer VoIP applications based on three commercial deployments, Voice Plus is a carrier-grade, pre-built VoIP solution for Internet-based service providers (ASPs, ITSPs, ISPs) that want to deliver IP-based voice and other multimedia services to their customers over cable, DSL, WiFi, or other broadband access networks.
Ubiquity has a growing, positive reputation from everything I've seen. Might be worth some exploration.

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