Special Report: Doing Business With No Walls <em>Entrepreneur's</em> guide to fully mobilizing your business--including the best gizmos to get the job done.

A computer, a telephone, a personal assistant: The 21st century mobile phone is all of that, and more. Now Entrepreneur offers a guide to fully mobilizing your business--including the best gizmos to get the job done.

The first indication that Doug Sohn runs an old-school operation is the sign in front of the cash register at Hot Doug's, his "sausage superstore" in Chicago. It reads "Cash Only," and Sohn means it. If a customer protests, he might chide them: "Didn't your mother tell you to always have $20 in your pocket?"