I also work in IT. I haven't had to be on call during a vacation in a lot of years. Where I work now we schedule our on call rotation around vacations. Our management is pretty conscious of the value of free time. My manager likes to say he's protective of his vacation time. Good for me! So when I'm on vacation, I really am.
That said when I've had to be on-call during a camping trip I was generally able to work issues on my own schedule. More often than not it was simply walking someone through something over the phone.
And yes, I was constantly conscious of being on call. It's not really a vacation if you have to work. I just could never relax in those situations.