You wouldn't be taking anybody's job if you go to SW. You will be filling a slot that you earned. If you decide to move on to UPS, you will be taking another slot that YOU earned. SW will replace you in a heartbeat and they will have spent only a few bucks to train you, and will have earned a profit from your labors every day you are there on the line. Don't worry about SW or those hoping to go there, do what is best for you.

Seriously, don't wait around for a call that might never come. You will regret it.