There are two kinds of membership.
1, When you download and install the software you create a free user account. This free membership makes it possible for you to buy cards using tickets.
2, If you want you may sign up for a subscribing membership which is rebilled every 30,90 or 180 days. This subscription gives you one new full card every day for free until you have all of them. During this period you may also buy extra cards using tickets.
So... YES you need a membership! BUT you don't need a subscription ;)
Hope this answers your question... God knows I've been nagging Totem to clarify this info on the Buy Girls page and on the Help page since the early beta testing last year! ;)