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+

SIP and mobile calling and messaging User Agent for Android based on baresip libBSD-3-Clause

baresip

SIP and mobile calling and messaging User Agent for Android based on baresip libBSD-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

PilferShush Jammer

Block unwanted use of onboard microphoneApache-2.0