You need to apply for an OIC in writing using IRS Form 656. If you have questions about your OIC application, call the IRS Centralized Offer in Compromise unit at (844) 805-4980. It may take the IRS up to five months to start to work on your OIC application. Once the IRS starts your OIC investigation, the OIC examiner will give you a phone number and extension to call to get information about your OIC.