This method with a linux machine :

- Export all you contacts y vcard, V3.0
- Copy to you Linux machine
- Execute the bash (see at bottom)
- Copy the file generated at ~/Contacts.cvf by blutooth or by scp to your Jolla
- Open the Configuration tool -> start contacts -> import from file

- This worked for me, import all my contacts in few seconds.
- Can be, you can execute this code in the N900

The bash code :

#!/bin/bash

TARGET="$HOME/Contacts.vcf"
rm $TARGET

FILES=`ls -1|grep -e "vcf$"`

SAVEDIFS=$IFS
IFS=`printf "\n\b"`

for FILE in ${FILES}; do
echo "Processing file ${FILE}"
cat ${FILE} >> ${TARGET}
printf "\r\n" >> ${TARGET}
done

IFS=${SAVEDIFS}