iPhone 4S and 5 freezes after not answering 2 calls I'm having some issues after receiving 2 calls from anyone. So this is how it happened:

(NOTE: This errors happens when my iphone is locked and the screen is turned off)

Sometimes people call me when I'm busy at work and I can't answer them. After receiving 2 or more calls from anyone, the iPhone freezes when it displays the message: "Do you to send a text message?" 

At the first time I can press the "Cancel" option. However, after receiving the second call it displays the same message but it freezes immediately. I can't do anything unless I make a call using Siri. When Siri calls, the iPhone "unfreezes" itself. I tried making 2 calls to an iPhone 5 and an iPhone 5C and the same error occurs.

It seems this is an OS error. Have anyone noticed this? Does someone know how to fix this error? 

Thanks!
After spending quite sometime trying to find out a definite solution to this annoying problem I am afraid this is a glitch we have to live with until apple comes up with a fix. In my case not even using Siri for a call helped out. Once the call is over the phone freezes again. The only walk around I have found is asking Siri to open any application I have in the phone (I usually ask for the calendar) and Siri will notice that the phone is locked and will ask for the four digit code to unlocked. Just plug the code in and magic, you will gain access to the phone without having to reset.