I use my cell phone and tablet for work. how much of my phone bill can i write off if any?

[Hal_Al]

Probably none.

The costs of a cell phone  may be a business expense, but only the additional costs in using a cell phone for business are deductible. If you pay a flat rate on a phone used for business and personal calls, the tax court has held that the flat rate is for your personal phone and you incurred no additional charges for business use. You have no deduction. (TC Memo 2007-151).