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 second telephone landline specifically for your business, its full cost is deductible.