What is the phone number to the IRS?

IRS E-file Help Desk number: 1-866-255-0654 - For e-filing assistance.
Tax Practitioner Hotline: 1-866-860-4259 - Tax assistance for Tax Preparers.
Tax Assistance: 1-800-829-1040 - Tax assistance for Taxpayers.
TeleTax: 1-800-829-4477 - Service that provides both recorded tax information and automated refund information.
IRS Business Assistance: 1-800-829-4933 - For assistance with completing Business Returns.
Refund Status: 1-800-829-1954 - To check the status of a Taxpayer's refund.
Social Security Administration: 1-800-772-1213 - For assistance with SSN's, ITIN's, etc.