Do I deduct the full amount of my internet/phone bill to my business expenses or only deduct half of it since I use it for both personal and business?

[Opus 17]

You can only deduct ordinary and necessary business expenses.  If you have an expense that is both personal and business, you can only deduct the amount of the expense that can be directly allocated to business use.  If audited, you must have some type of reliable method to determine the cost that you allocate to the business, otherwise the IRS can deny the expense.  It might be 50%, if you can prove that 50% of your use is for your business, but it might be more or less, depending on what you can prove with some kind of reliable records.