I am applying to do a master's thesis at a German research institute. The institute's website encourages applicants to contact the researchers directly (and does not give more information about the application process). I have been wondering whether initiating this contact over phone could be a way to make a strong first impression, and would make it less likely that my subsequent application mail will disappear in their inbox. The goal of the phone call would be to ask whether their group has an open spot for a master's student etc. On the other hand, I am worried I would be breaking some social code by making such direct contact with someone 'higher up in the hierarchy', or that they would think I am wasting their time by calling in person.
So, my question is: Would it be appropriate to phone a researcher/academic with such inquiries?
I realize this will depend on the person being called, but I think it is still possible to answer whether this is generally acceptable within cultural norms.
Note: Many, but not all, of the researchers list a phone number on the institute's homepage.