There was a sockets API though (https://en.wikipedia.org/wiki/Winsock) and IIRC we all used Trumpet Winsock on Windows 3.1 with our dialup connections. But could have been 3.11 - my memory is a bit hazy.
Schedule+, which was contained in Windows for Workgroups 3.11, contained address book functionalities that were clearly better than Cardfile.
But people used Cardfile for many other different purposes than serving as an address book.