I would like to ask if there is one of these Api: SIP RTP SRTP ZRTP for iPhone, if there is a way to use them in iPhone Simulator, and what is the default gateway in iPhone.
SIP
RTP
SRTP
ZRTP
A very nice framework for voip pjsip , which is open source under a dual license (free and commercial) and provides SIP / TLS and SRTP support.
ZORG is an open source ZRTP implementation as well as a pjsip integration .
None of these are built into iOS. There are several SIP applications, but I believe the developers of these applications had to write their own C / C ++ libraries for these protocols.