Hi.
Sadly it seems the Forticlient does currently not support IOS together with client certificates.
I followed the official certificate deployment instructions to store the certificate file on iphone and I am not able to select the certificate permanently in the connection settings/profile. After selecting the client certificate and hitting the save button, I may return to the config page and the certificate field is again emtpy. Of course establishing a SSLVPN tunnel fails as well.
I verified the behavior with iPhone 4S & iPad 2. Works great on IOS 5.1, definitely not with IOS 6.
With best regards
Bax