I thought that in my state at least, you HAVE to put your office number on any advertising....

I will try and look up the rules again to see.

In New Jersey you do have to put your office phone number.

In my state you don't have to put your office number on your business card. In fact my office has switched over to OneCall and wants us to use the assigned phone number so that our calls follow us wherever we are and to put that on the business card and yard signs, not our office number. I'm not going to do that for the reasons many others stated. I want my number to follow me when I leave my broker, so the phone number needs to be one I own. My cell phone is always with me, so to me it serves the same purpose as OneCall. For the same reason, I put down my personal e-mail address.

As for whether business cards are used for clients or other agents, I use them for both, but about 80% go to other agents or are left at showings and about 20% go to clients.