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Our application was built as an Android application coded in Java. It leverages a SQLite database to manage all contact information, messages, etc. It makes use of a data connection in order to communicate with other parties. We chose Android as it's a rapidly growing, already very common platform with good flexibility. (And it's more pleasant to code for than the iPhone!) Mobile platforms offer interesting use cases, due to limited screen size and the use of touch screen interaction.
We used standard toolkit for many of the UI components. This was done for ease of development as well as usability reasons. Using standard components that users are used to seeing will help to decrease the learning curve and help prevent misunderstands, errors, etc.
We created custom colored images to represent different ideas throughout our interface. This was done with freely available images which were then colored, scaled and composed to give the desired resources. Doing this right was very important to our usability. I believe the icons we created and used added a lot the the user interface. They were good at conveying their contained concepts (trust, warnings) in a concise fashion. Also, they gave indications without relying solely on color, so that color blind users would still be able to use the interface effectively.
Individual tabs in the UI were defined as separate Activities, which helped allow the team subdivide tasks across each of screens. This is a robust part of Android and so is very responsive and usable.
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