I think “PortaOne vs. Nextone” is not the right question, in most areas they are complimentary to each other. E.g. MSX is a good SBC/carrier switch, and PortaOne provides real-time billing for it (PortaBilling for NexTone). On the VoIP side MSX is mainly class4 switch, while PortaSIP is class5 (i.e. you need PortaSIP to do fancy stuff with your IP phones such as follow-me, music on hold, etc.) – so you probably need them both if you want to run something like Vonage solution.