Abto multi account sip dialer app for iPhone and iPad

ABTO Softwares VoIP SIP softphone.
Can be used to call sip numbers and landline numbers (if sip provider has this option).

Features:
voice calls;
video calls;
text chat (based on SIP MESSAGE request);
works with all popular SIP servers, including Asterisk/FreeSwitch;
make direct calls between clients without SIP server;
allows to use UDP/TCP/TLS protocols for SIP transport;
ability to make secure calls using SRTP;
supports STUN/ICE;
IPv6 support;
CallKit - native incoming call UI and system integration of VoIP calls;
2 simultaneous calls;
call conferencing;
attended transfer;
4 concurrent accounts.