Unfortunately the odds are this one is calling from outside the country so the USA authorities cannot do a whole lot unless they can find any of their associates in this country. And even then I would not know what charges would be filed (I am not in Law Enforcement).
Do not answer calls you don't know and never call them back. The IRS will not call you. 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. This is a SCAM.