If you have separate personal and business lines (which accountants recommend), this is easy. If not, you can still come up with a figure. Add up a year's worth of monthly cell phone, long distance, phone card and roam charges, and figure out what percentage of it pertains your business. Don't forget to include the cost of the phone itself. Fax machines and fax lines (or your bill for faxing at Kinko's) go here, too.