if you are looking for the main telepone number for the irs for taxes, this is the 800 number

Telephone Assistance for Individuals:

Toll-Free, 1-800-829-1040

Their hours of operation are : Monday – Friday, 7:00 a.m. – 10:00 p.m.
your local time (Alaska & Hawaii follow Pacific Time).

they are closed on saturday and sunday.