Incoming call controls can be modified on jailbroken iOS devices with the tweak Cou. Once installed, Cou changes the steps required to decline an incoming call. Instead of a "slide to answer" slider, the user is presented with two individual buttons, Decline and Accept.
Tapping Decline will have the same effect as pressing the power button twice, which declines the call. This can make it faster and easier to decline a call, however the buttons can also be accidentally pressed more easily. Cou provides a toggle to enable or disable the tweak entirely.
Other settings include the option to hide Message and Remind options on the incoming call screen. Normally, these options are displayed, offering additional ways to communicate when a call can't be answered immediately. To simplify the incoming call screen, each of these options can be toggled off under Settings -> Cou.
Cou is available on Cydia from the BigBoss repository for free. Jailbreak iOS 7.1.x with Pangu to start customizing iOS. Check here for instructions on how to jailbreak iOS 7.0.x with evasi0n 7. You can also find out how to purchase and install Cydia tweaks with this guide.