There's a bug in iOS 7 that will let anyone make a call from your phone even if it's locked with a passcode.
The glitch was discovered by a Palestinian man and first noticed by Forbes. If a phone is locked, you can still tap the emergency call button to pull up the keypad. Normally, this only lets you call 911. But if you type in a regular phone number and hit the call button several times repeatedly, the call goes through anyway.
We independently tested the bug and it definitely works. We only had to tap the call button a few times.
Here's a video of the bug in action: