They (the scammers) prefer untraceable means of payment.
The IRS will not call you. They send letters via US Mail. The IRS won't ask you to pay in i-Tunes cards. The IRS will not wish you "good luck as the situation unfolds". Trust yourself and your instincts - do not let a bully intimidate you by threats that are nothing but hot air (and bad breath). This is a SCAM.
Do not answer calls you don't know and never call them back.