Yes, a few things, like
in Internet Explorer, you have to click the little plus over the call button, to activate the Zoiper plugin.
When you import subjects from a text file or Excel file, you need column headers in line 1 for it to happen.
You can only import 5.000-10.000 subject pr import, depending on their property richness.
If you import an Excel file, you need to make sure it really is an excel file and not just a .csv file renamed to .xls, just open it in excel and save it as an excel file, if you run in to that problem.
You should always copy projects and users in the system instead of making a new.