We've already had a chance to review Fake Caller, but with the popularity of these fake out apps, it was worth checking out Fake-A-Call. This app offers a similar idea for free and doesn't do to bad.
You won't find nearly as much customization as you will with Fake Caller, but it definitely handles all of the basics. The main screen will give you a settings tab, a get started tab, a toggle switch for vibration, and a timer with a dial underneath to set the appropriate time. Before you get started, you'll want to enter into the settings tab.
In settings, you can enter the callers number or name, what type of call it is, change the background from a few preset options, and select from one of five different ringtones. The backgrounds and ringtones are really where this app falls short as you can't use anything that you already have set on your iPhone this is frustrating and detracts from the reality of the app.
If you've got the time tab set to on and everything ready to go, the app will do it's thing if you press the get started app and then leave your phone alone. It's not something you can easily set up on the fly, so you're pretty much stuck with your phone being useless until it's time for it to go off. Considering this app is free, it's definitely worth trying out, but it's most likely going to disappoint.