How are "emergency calls" restricted? An "Emergency" link on my iOS 7 lock screen goes to a phone dial page that says "Emergency call". What are the restrictions on this page? Can anyone use my iPhone to dial out? Does it only work with emergency numbers (e.g., 911)? Is there a time or use limit?
The emergency call function only allows dialing emergency numbers valid for whatever area you're currently in, i.e. 911 in the US, 112 in the EU, 999 in the UK...

See the iPhone User Guide for more details.