Many small law firms using Macs use Marketcircle’s Daylite program to manage their contacts, calendars, tasks, etc. For example, here is a post by Ben “The Mac Lawyer” Stevens talking about how he uses Daylite.
At Macworld Expo, Marketcircle is currently showing off an upcoming iPhone app called Daylite Touch which allows users to access most of the key data on Daylite from the iPhone. If your law firm uses Daylite, check out this video interview of Marketcircle CEO Alykhan Jetha by TUAW.