What's an "acknowledgment"? (I'm clueless as to how all this 121 stuff works, as you can see.)

This is what I think I understand so far:

1.) If you are on your off day, never answer your phone. Period. Unless you want to fly, that is.

2.) If you are within your RAP...aren't you pretty much obligated to accept anything they give you, as long as it won't violate 117? What's the advantage of not answering the phone and calling back within 10 minutes?

3) If you are on a trip, again, same question applies. You're on duty, so...don't you have to accept whatever they give you, as long as it's legal?

4) If you answer the phone, and you're within your RAP or on a trip, and the assignment is legal...you have no basis for refusing the assignment. Right?

I get that you have to protect yourself against a request that would cause you to bust 117. I also get that you should never say 'Yeah, I can be there in less than 2 hours' while on short-call reserve. But I guess I don't understand the advantage of ignoring the phone call from CS while you're either inside your RAP or on a trip...?