You can use several services on iPhone ( iOS )
Cisco VPN on iPhone / iPad / iPod ( Recommended )
Cisco VPN is an SSL VPN Services. Its purpose is to be a secure, small, fast . Data transport over TCP (HTTPS) or UDP (DTLS or ESP).
Open VPN on iPhone / iPad / iPod ( iOS )
You can use Open VPN in 2 ways , depending on your location internet service UDP or TCP