The only certificate Nokia has for 3rd party application is Nokia OK. Nokia OK can be received through Nokia OK program. More information of the Nokia OK can be retrieved from the Nokia Developer ProPoint.
The Nokia 9210 Communicator supports only Nokia or Nokia OK certificates. Nokia certificates is only for Nokia software and Nokia OK for Nokia OK 3rd party applications.
Nokia 9210 Communicator does not support any Symbian certificates in application installation.
Technically the procedure is following: When creating a software installation package (a. k. a. SIS file) the path to the certificate with required parameters are written to the PKG file. More information about creating SIS files can be found in SDK documentation.