Preshared key exchange

I have to exchange many sensible data with some partners. They are international phone companies.
But, no one knows about public/private key pairs, nor PGP/GPG.
All VPNs I set up are using PSK, no X.509 certificates.
Event gpg data are encrypted using symetric keys.
If someone knows why ?

iRubik

c'est fou quand même ...