1 800 829-1040
Be prepared; If you owe the IRS, they will ask you who your employer is and where do you bank.
Remember it is a Federal crime to lie to a Federal Agent. Are IRS customer service agents considered Federal Agents? I wouldn't want to be the one to find out.
Answer each question honestly. Try not to volunteer information unless you are sure it will help your situation. Often times volunteering information leads to additional questions that may not be helpful to your case.
For help with past due tax returns, visit http://taxeswilltravel.com/pdr.htm