I create a spreadsheet where I record all the monthly charges related to the cell phone line that we use for the business (Line charges, Equipment charges, surcharges/taxes/fees) add those up and multiply by the estimated percentage the phone is used for business purposes other than personal calls. I use 25% and enter 25% of total charges for that line in the Communications expenses (4th down) under Business Expenses. I also include the yearly fee for the business land line.
