Currently baresip VoIP User Agent app supports SIP voice calls and
messages, voicemail Message Waiting Indication (MWI), and incoming call
transfers via REFER method. Voice can be coded using PCMU/PCMA, Opus,
G.722.1, and iLBC codecs. Security is achieved via TLS signaling
transport and ZRTP and (DTLS) SRTP media encapsulation.

Development of this baresip app is motivated by need for a secure libre
software SIP User Agent for Android that does not depend on proprietary,
third party push notification services.

Source code available at https://github.com/juha-h/baresip-studio,
where issues can be reported.