While robust, the free version does have restrictions compared to the paid "Biz" or "Pro" versions:
Zoiper 3.15 supports both SIP and IAX2 protocols. SIP is the industry standard used by most VoIP providers, while IAX2 is often used with Asterisk-based PBX systems. This dual support ensures compatibility with a wide range of services. zoiper-free-3.15-setup.exe
Unlike modern “freemium” softphones that limit call duration or account numbers, version 3.15 gives you full calling features without expiration — just a non-intrusive “Powered by Zoiper” voice prompt at the start of each call. While robust, the free version does have restrictions
Pro tip for tinkerers: The 3.15 installer still works on Windows 10/11 (compatibility mode if needed). It’s lightweight (~12 MB) and can run from a USB stick as a portable app. Pro tip for tinkerers: The 3