In most cases, you can't deduct a cell phone as a work expense at all.
You can deduct a cell phone bill if you use the phone exclusively for work. You can depreciate the cost of the phone if you use it exclusively for work.
If you use the phone more than 50% for work and less than 100%, you can depreciate the percentage of cost equal to the percentage of business use, but only if you can prove by your call records and data logs that you really do use it more than 50% for work. If you use it less than 50% for work, you are not allowed to deduct any of the phone cost.
If you use the phone less than 100% for work, you can deduct the percentage of the monthly bill that is for work but only if you keep phone records of every call, and are on a plan that pays by the minute (not a flat fee) and only deduct the minutes for business use. Since a flat rate plan charges the same whether you use the phone 1% or 99% for business, there is no way to attribute the cost to business, so flat rate plans can't be deducted at all.
HOW to deduct depends on whether you are self -employed or an employee. If you are a W-2 employee, go to the section for job-related expenses on the deduction and credits page. You can enter the bill as an expense and enter the cost of the phone as an asset (assuming you qualify as described above).
If you are self-employed you deduct the expenses on schedule C, as an expense or asset, if you meet the rules mentioned.
