Your clients will want to know where your office is, if it is convenient to them, and how to get there.

They can get directions from whoever answers your telephone, but a preferred (& more cost effective) approach is to look to the internet - it's not like they've actually asked for directions.

The yellow pages are one way to give them that information, either using the book or the on-line version.  However, the yellow pages also give the information to get to your competitors.

Having contact information and directions on your web site provides people with the information they need to find you and not information on finding other lawyers.

Legal Firm Web Host semi-custom and custom solutions can have a Google map right on one of your web pages (after all, you do not want a potential customer leaving).