The toll-free number for IRS customer service is 1-800-829-1040 as of February 2015. This number is intended for people who file electronic returns via a preparer or online program. Those people should not use the number for the IRS e-help desk, which is 1-866-255-0654.
The e-help desk number is for enrolled and reporting agents, certified public accountants, software developers, and other people who have issues with electronic filing products.
The IRS warns that wait times for telephone help may be extensive, and the agency cannot help with some issues over the phone. The IRS recommends that taxpayers use the IRS website if possible. The hours for the customer service number are 7 a.m. to 7 p.m. local time, Monday through Friday.