Tried to do the exactly same thing I guess - install new root certificate authorities to my 3650.
I tried uploading the certificate to my BSD box with the .cer files MIME type set to application/vnd.wap.wtls-ca-certificate as the nokia documentation suggests. In addition I used the download page template from document: Nokia_WAP_Phone_Security_v3.2_en.pdf
But when starting the download (I'we tried WAP browser, Opera and Doris) the phone only tells me that unknown/unsupported file format.
So if there's further info on the subject somewhere, please help
I haven't had the time yet to play with the Nokia SDK certificate store creation tools,
but I think they might do the trick. It seems that the certificates need to be packaged
in a format compatible with Symbian using the SDK and then stored in the phone.
I will post more finding regarding this matter as time permits.