The customer service number for the IRS is 1-800-829-1040 as of February 2015, and the customer service number for businesses is 1-800-829-4933. Representatives can help from 7 a.m. to 7 p.m. local time Monday through Friday, although the IRS warns of long wait times.
Over the phone, customers can ask questions about notices and preparing their tax returns. However, much more help is available online, and if a customer calls again, he cannot speak to the same person he previously did. On the IRS site, customers can establish payment plans, make payments, check on refunds, receive tax return transcripts and read answers to most tax questions.