I still have a perfectly working Windows Mobile PDA-phone. I use a program called PIM Backup to make backups of the databases such as calls, SMSes (text messages), contacts, calendar, …. The program can generate either a binary backup, or a more readable backup. I use the latter one, so I could unpack the backup on my desktop computer and use it as an archive. The generated backup files have a .pib extension. The file itself is a ZIP-file containing the different parts of the backup (calls, contacts, …) as separate files.