Don't deduct a telephone landline, but …
You can't deduct the cost of your main home telephone landline, even if you primarily use that phone for your business. The IRS says that the first hard-wired phone line in your home is considered a nondeductible personal expense.
But you can deduct as a business expense the cost of business-related long-distance charges on that phone.
If you are an employee, they would be claimed as an unreimbursed business expense on Schedule A.
If you are self-employed, you would count the phone calls as an expense on your Schedule C or C-EZ.
And if you install a 2nd telephone landline specifically for your business, its full cost is deductible.