While some aspects of the phone - mainly the radio stack - remain closed, you can build and deploy new kernel images. The Greenphone’s SDK contains the tools you’ll need to create your own applications, with the ability to test them inside the SDK before delivering them to a Greenphone. Applications developed on the Greenphone should run on most QTopia hardware. Trolltech provides three levels of access to the Greenphone source code. Community developers only get the code for community developed applications, while paying a fee gets you access to the QTopia application suite. If you want access to the OS code, then you’ll need to sign up for Trolltech’s partner program. Most developers will find the basic community access good enough, especially if you’re using the Greenphone to familiarize yourself with QTopia and Linux mobile application development or to build your own custom suite from existing apps.

Trolltech has software partners lined up: the RealNetworks Helix DNA media framework is available, Tao is working on a JVM and Quickoffice is being ported this year. There’s a handful of applications and utilities on the Qtopia site, including flickr uploaders, a music player that supports Ogg Vorbis as well as MP3s, drawing applications and a sound mixer. If you dig through the Trolltech bogs you can find a version of the Dasher gesture text input tool. The Greenphone runs a more recent version of QTopia than the Linux-based Sharp Zaurus, so you’ll need to port Zaurus.ipk files, which isn’t trivial but gives you a choice of many applications from programming tools to HTML editors to games and utilities. Another option is to install a scripting language like Python. You can use it to run a wide range of existing applications - and develop your own without delving into the depths of C++.

If you are going to write your own apps from scratch you’ll be working in C++, using the QTopia libraries to handle displaying user interfaces and accessing operating system functions. Trolltech’s own Designer is intended to help build phone user interfaces, and works much like any form design tool. Once you’ve laid out the user interface, you can start building your code. Compilation is slightly different from building a C++ application for a desktop Linux, while the online documentation explains the steps clearly enough.

Even though you can install a reasonable choice of applications, the Greenphone is most definitely a developer device. The phone’s basic suite of applications is crying out to be extended and even replaced. There’s sample code, tutorials and forums on the Qtopia.net site, with plenty of community support. Keep an eye out for regular firmware updates, as Trolltech is fixing bugs and adding capabilities to the Greenphone, as well as opening up additional device APIs.