Ok, so I figured it out...if you have the ringer turned off on the phone it will only give you the option to answer, when ringer is turned on, you get both options, Decline and Answer
1- Simply tap Decline while you are using iPhone. 2- Double-click the Sleep/Wake button on the top of the phone. 3- Press and hold the mic button on the headset for about 2 seconds.
Any of these 3 options will immediately silence the phone and send the incoming call to voice mail.
If you want to take it one step further, you can block calls and keep your Wi-Fi access to the Internet, too. In Settings, turn on Airplane mode and then tap the Wi-Fi to get it started.
JailBreak your phone, install EZDecline - which will give you the feature Apple should have given you, but didn't - the option to decline a call from a lockscreen.
