Please note that media (RTP) encryption is not any safer than unencrypted RTP without first encrypting SIP, as encryption keys are sent in SIP.
To encrypt SIP, just set your transport to TLS, and ensure you are sending traffic to port 5061 (rather than 5060).
Simply place the call with SRTP enabled.
Set your outbound proxy to secure-hosted.surevoip.co.uk, while keeping your registrar the same. Ensure you set the outbound proxy port to 5061, and transport to TLS.
For outbound calls, just place the call with SRTP enabled on your device. For incoming calls, please let us know that you would like to have SRTP enabled, and we will ensure calls offered to your phone have SRTP enabled.