This means that you should be able to support the business usage by texts, calls, applications, etc, that would provide proof of business use versus personal use. Time is also a factor when trying to determine the business use of your phone. The IRS expects you to be able to substantiate the percentage you claim that the cell phone is used for business. You ultimately decide the business use percentage based on the facts and circumstances as you know them.
Items of record could be advertisements with your cell number used and then jobs marked on a calendar each day that would prove the activity conducted for business and simply a log of the time you used your phone for business each day versus the time spent using your cell phone for personal uses. The message on the voice mail might be the business name and information.
Phone Charges: If you have a dedicated phone in your home or a dedicated cell phone just for business purposes, all charges can be deducted. If you use your regular home phone (only charges for extra services for business) or cell phone for business related calls, you can deduct a portion of your bill.
