How to purposely make your iPhone drop a call?

I'm trying to get my iPhone replaced. It's under warranty and in mint condition but the Apple Store won't consider my apps crashing and numerous problems with a way of replacing my phone. So I was wondering how I can purposely make my calls drop so that it shows them on the diagnostic that it has dropped calls in the past few days. I know it's a weird question but Apple is so strict now with replacing phones that even though my mint condition brand new iPhone 5s has problems, just because it doesn't show up on the diagnostic they won't replace my phone and I've already tried twice and have failed miserably.

Apps crashing probably has nothing to do with the phone, and probably has more to do with people writing buggy apps. Also any apps that haven't been upgraded for iOS 7 (like alot of free ones may not have been since they are free) may crash. Otherwise try to restore it, then install your apps slowly to try and determine which one is bad.