Set the initial activity screen to "InitialActivity"
This activity looks at whether the local storage contains a username/userID, meaning if the user is already signed up, then he will be taken to the contacts list screen directly (not yet implemented), otherwise he will be taken to the sign up (LoginActivity for lack of a better name) screen.

At the sign up screen, the user enters Gender and Country
Which is a POST request to the server
The server replies with a username and userID, which is stored into local storage (thus the next time user starts up the app, he is taken straight to the contacts list)