FYI: on iPhone, these 2 Apps are the favorite combination I am using for visiting blocked websites in mainland China:
Check OpenVPN + Ovpn Spider: Free VPNs for iPhone Users for how to use them together.
OpenVPN is for setting up OpenVPN VPN connection.
Ovpn Spider is for getting free OpenVPN profiles and accounts.
Another alternative free OpenVPN account source is Riseup (search and find it out by yourself).