Android: When you need to make a call, Slide Dial provides access with a single swipe, from anywhere on your phone. There's no need to switch to the home screen and then the dialler, or use the task manager. You can call up the dial pad from any app.
A swipe gesture from right to left or left to right calls up the a dial pad so you can quickly make a call, no matter what you are doing. Slide Dial is a very simple app that launches as a floating panel over the top of whichever app you happen to be using. You can choose which section of your screen is the hotspot so you can start the gesture from wherever your thumb naturally falls -- launch the service after installation and then access settings using the menu button.
Download a copy of the app from the link below. It supports Android 3.0 and above, and you'll need to enable third-party apps in order to install it.