OK. Encoding was the thing.
I first had to use UTF7 due to german Umlaute in the original data, but this leads to misinterpretation of the imported data when using Import-csv.
To avoid struggling with German Umlaute, e.g. with "Osnabr�cker Stra�e 77" instead "Osnabrücker Straße 77" when importing with Encoding UTF8, I have to convert the file to UTF 8:
Get-Content $csvimportfile | Set-Content -Encoding utf8 $csvimportfileutf8
Import-Csv -path $csvimportfileutf8 -Delimiter ';' -Encoding UTF8
Now I get the proper data format while importing:
Bob
+41 12 12345
bob@hallo.to
Osnabrücker Straße 77
Thanks a lot for your help :-)
Windows / Exchange / Lync/Skype Dinosaur