In order to have a custom splash screen, we just purchased Unity Pro. After all it says in the license comparison:
Custom Splash Screen
Instead of
showing the Unity splash screen when
your application starts use your own
splash screen or none at all!
Now, I still cannot specify splash screen.
[38683-screen+shot+2015-01-13+at+11.04.23.png|38683]
What gives?
You need that iOS Pro license, you can read the comparison table to see that the splash screen is customizable only in iOS Pro 
To make use of Pro features in iOS/Android, you need iOS Pro/Android Pro, respectively.
What does "Custom Splash Screen Instead of showing the Unity splash screen when your application starts use your own splash screen or none at all!" mean then? This is stated for Unity Pro. It says nothing about iOS or Android.
– UmaiOn the same table choose the iOS option from the top and you'll find all the features that come with iOS pro. Unity Pro only includes PC, Mac, Linux, and Consoles as platforms and iOS requires a separate license called iOS pro along with Unity Pro. Every other platform that is not included in Unity Pro and requires its own Pro plugin license is listed separately there.
– HarshadKThat would be a custom splash screen for PC/Mac/Linux/Windows Phone/Blackberry etc. multiplatform builds that are supported by Unity Pro. (go to https://store.unity3d.com/ and click on "Read More" to see the list of supported platforms). Android and iOS require their own pro add-on.
– tanoshimiOk, I'll accept that. I still think iOS is not included is NOT stated on the Unity Pro page very clearly. After all, the Apple logo is visible there.
– Umai
Do you have the Unity iOS Pro license? Because it seems like you only bought the Unity Pro license without the iOS Pro.
– MangasNo I don't. Sure that is the problem here. However, the Unity Pro license sounded much like it would be enough. Looking in the details of Unity Pro - the license comparison, Deployment section: "Custom Splash Screen Instead of showing the Unity splash screen when your application starts use your own splash screen or none at all!".
– UmaiYes. However I insist. The Unity Pro has that line in Deployment section: "Custom Splash Screen Instead of showing the Unity splash screen when your application starts use your own splash screen or none at all!" - what would that mean?
– Umai