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Connect your iPhone to USB and open using iTunes application.
Select your device -> "Apps" section -> scroll down and you will see a list of applications that have a shared folder.
Import a file named "cachain.pem" containing the whole certificate chain, from Certificate Authority Root down to server certificate, including intermediate CA, using PEM format (ASCII format, starting with line "----BEGIN CERTIFICATE----").

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Nokia devices accept certificate in DER format (binary format, non ASCII as PEM). Remember to use a DER format certificate, otherwise Nokia phones will not recognize it properly.
You can install a new CA root in three ways:

• Point your phone's browser to the CA root certificate URL
• Send the certificate via Bluetooth
• Copy your certificate to the SD and open with a file manager application

You will be prompted to trust the certificate. PrivateGSM can now connect to your server.

 Restrict Certificate Authority

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Import a custom CA (see 9.2.2"Custom CA on iPhone"). Open and edit Sip settings, and set to ON setting named "Enable custom CA root"

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Import a custom CA (see 9.2.3 "Custom CA on Nokia"). Open Settings -> Advanced Settings -> TLS Settings and set to ON setting named "Enable custom CA root"