I am applying for admission to a history PhD program in the UK, and other places as well. Is a face-to-face interview required, or do they allow the use of Skype? What about American universities?

I've also heard that not all universities even require interviews and base acceptance or rejection purely on the application packet. Has anyone heard of this?

Hello in my applications to a couple of universities I was invited to both face-to-face interviews, but more commonly to phone interviews (actual phone not even Skype...this was 2 years ago). My suggestion is that if you have a telephone interview and get accepted, do try an visit the university for a day or 2 before you actually start. I actually did this and I found it to be good practice as I knew what I was getting into, and it was also looked favourably by my supervisors.

Yes, I do know people who had PhD interviews over Skype. Some don't require interviews at all and will accept or reject based on the application. There is wide variation. Good luck. :)