Here is a script that will convert a CSV file to a bookmark.txt file for use with navit. To convert from vCard, it can be used with the vcard-to-geocsv script.

The CSV should look like:

name,latitude,longitude
"Doe, John",40.2553,-60.1552

The resulting bookmark.txt looks like:

mg:-60.1552 40.2553 type=bookmark label="Doe, John"

Note that navit may automatically convert the coordinates to a hex value the first time it runs after using a bookmark.txt file generated by this script.