How to add certificate to P800

I try to add a self-signed certificate to P800: I just send the
certificate using Bluetooth to P800 and the phone shows certificate
contents and gives possibility to either add the certificate or
cancel. Adding certificate fails (unable to add certificate) without
giving reason.

The certificate is taken from MacOS X keychain and seems to be in some
binary format (DER ?).

Does anyone know if it is even possible to add a self-signed
certificate to P800?

-- joonas