Glacier Dial: Secure Phone

Glacier Dial: Secure Phone is a free and open source VoIP softphone based on the SIP protocol, and that is based on Linphone for iPhone
Source code available at https://github.com/GlacierSecurityInc/GlacierVoice-iOS
Glacier Security, Inc. is a full-service SaaS provider of secure messaging, secure voice and device management solutions for mobile and wired networks. We empower our clients to work in nations throughout the world with confidence that their associations, communications, devices and intellectual property are protected.
Features, Security, & Privacy:
- Encrypted 1:1 and conference calling between Glacier users
- Virtual anonymous number with customizable area code for external Glacier calls
- Zero touch setup without phone number or e-mail address
- No metadata collected or stored
- Open source code for transparency and audit

Requirements:
- Corporate or organization subscription
- Some deployments require Glacier Security or your organizations Mobile Device Manager (MDM)
Wait, there's more:
The Glacier network is deployed unique to each customer with cloud based immutable infrastructure leveraging concepts of Moving Target Defense (MTD). MTD adds uncertainty and diversity to our networks, reducing the surface area of attacks to provide true private and anonymous communications.
You can deploy an app or you can deploy a full service solution.