For the majority of web apps and mobile apps, two of the primary calls to action on the landing page or welcome screen are Sign In (aka user login) and Sign Up (aka user registration). 

For the Skype iPhone App, there is a glaring omission of a user registration call to action on the welcome screen: 

This is really bad because the app is missing out on acquiring new users who download the app but have not yet registered. Here, Skype is making it mandatory for the user to go to their web site in order to register — and to make matters worse, it’s not even clear to the user shown the screen above that they need to go to the web site. Ideally, Skype should have another call to action allowing the user to register in-app. Even if it is a partial registration that requires completion through the web (non-mobile) flow, it is much better than nothing. 

Here are some other iPhone apps that capitalize on the opportunity to acquire new users on the welcome screen: