This number is designed for international taxpayers, and it seems to be best used either by American ex-pats living overseas or businesses working with workers who are citizens of other nations. When I dialed this number, I was given the standard IRS question of English or Spanish, along with an alternate number to call if I was looking to get assistance with COVID relief stimulus funds.
As neither of those applied to me, I was taken to the next menu, where I was told that I could ask questions about getting an individual tax identification number, questions about employment that needed to be sponsored in the United States or business questions about an individual. This related to form 6166, which would confirm that the individual in question is a resident of the United States for tax purposes.
I hit the button for an individual TIN, and was told I would be transferred to the next available representative. After a hold, I was told the wait time would be between 30 and 60 minutes. I was then put back on hold and given the option to either continue waiting for my place in line or request a call back when it was my turn to speak with someone.
I opted for the latter, and about 45 minutes later, I received a call from a number whose voicemail confirmed that it was the IRS calling me as it was now my turn in line. As I didn't need to get an individual TIN and certainly didn't want to provide my personal information to the IRS for a request I didn't actually need, I ended the call there without pursuing further action.
Overall, I think this phone system is relatively well set up and straightforward. There isn't much in the way of information on this number, so you need to know what you're calling about before you try to use this number. You aren't going to find any guides on what you might ask for, nor will you find any ways to get to any other departments of the IRS' phone system.
The use of a call-back feature that actually works is a major positive. One of the most frustrating things about calling an IRS number is how long the wait time can be, and having a call-back feature helps take care of that. That said, if you're not an international taxpayer and don't work with international taxpayers, you aren't going to find much use out of calling this number. As this number has a specific purpose, it should only be used by customers who fulfill that purpose. If that doesn't apply to you, you will find no benefit to calling.