OK I'm making a strange suggestion but you might want to take a look at this.
Fastmail.fm is an email service. However, they offer one of the best address books out there. It has customizable fields .... everything. I had given them a lot of input into their address book based on this now-defunct package that I used to love. They implemented all but one of my suggestions. You can put in anniversaries and birthdays, but not as reminders.
However, it's kind of weird logging into an email service just to access an address book. :D So that's why I'm going to recommend Airset (www.airset.com). I've been using it for quite some time for phone alerts, but I think it will have everything you need! Very nice interface, calendar, contacts, notes, birthdays, you can make groups, many things....