Natterbox is described as 'leads the way for telephony within Salesforce!'. There are five alternatives to Natterbox for a variety of platforms, including Windows, iPhone, Mac, iPad and Linux. The best alternative is Asterisk, which is both free and Open Source. Other great apps like Natterbox are RingCentral (Paid), miniSIPServer (Paid), Slingshot VoIP (Paid) and 8x8 Virtual Office (Free).
You will be able to setup your own VOIP system in ONE HOUR. miniSIPServer can run on Windows, Linux and even Raspberry Pi. We can also run it on kinds of virtual machine systems, such as Hyper-V, VMWare, KVM, Xen.
Slingshot VoIP is a cloud-based communications provider that specializes in business VoIP service. Our platform delivers carrier-grade services including virtual PBX solutions that caters to small and medium sized companies.