I don't do detailing as my line of work, but I am INC'd for my line of work (music business, production manager, instrument tech), and you can write this stuff off if you are running your own business. Currently the tax code is kinda a gray area pertaining to cell phones. It used to be if you had a home phone (whether it was a business line or not), it couldn't be deducted, but your cell phone could be. Now since more people are ditching the home phone for cell phone, it's a gray area. If your accountant is worth is fee he'll make it work for you. What they do is a depreciated value over 5 years of the equipment, and write it off your taxes. Then they can take a percentage of your phone bill (as long as you use it 51% for business purposes).
Besides this, you can write off your mileage at 55 cents a mile this year I believe, any maintenance that was done to your vehicle can be wrote off. Anything for work clothes (uniforms), materials such as polish. Lodging if you did an out of state detail, meals those days are covered by a Per Diem the IRS allows, etc. Writing off your internet service at home can be done too, but it's a hard to justify one, cause would you have it if you didn't do detailing? Probably, but if you are a work from home cyber commuter for at least half of your job, you can!
And I can't stress this enough, KEEP ALL YOUR RECEIPTS. You may never need them, but if you get audited it's good to have your butt covered. Start adding all your stuff up in a spreadsheet separated by different categories (Tools, Food, Parking, Cell bill, etc), and take that to your accountant and have them do the numbers. Well worth it.