Sipdroid

A SIP (VOIP) clientGPL-3.0-only

Linphone - open source SIP client

SIP (VOIP) phoneGPL-3.0-only

VoIP.ms SMS

Popular Android messaging app for VoIP.ms, a Canadian VoIP providerApache-2.0

baresip+

VoIP and mobile calling and messaging app based on baresip libraryBSD-3-Clause

baresip

VoIP and mobile calling and messaging app based on baresip libraryBSD-3-Clause

Simlar - secure calls

Protect your privacy with encrypted phone calls.GPL-2.0-or-later

aTalk

XMPP/Jabber client with encrypted instant messaging and video callsApache-2.0

ShizuCallRecorder

Empowers ADB through Shizuku to record phone calls on non-rooted device! GPL-3.0-only

Privacy Flip

Manage your device privacy based on lock/unlock stateGPL-3.0-only

PilferShush Jammer

Block unwanted use of onboard microphoneApache-2.0