Due to having no sockets support, multitasking or the ability to run native code, companies like Skype and Viber are sitting on the sidelines, preventing any true VOIP application on Windows Phone 7. So leave it up to someone at XDA to try and do it themselves instead!
Developer Jefis posted this today about the project:
Hello there fellow developers. I recently made quite a progress in developing skype for WP7.
I want to share my current progress with you, so maybe someone will want to join this little project, which, in future will be released for free, and probably with source code .
I'm not designer, as you will see from the screenshots, but, if you are, and want to join this effort in making skype, contact me asap.
Current status of project: Working contacts + ability to chat. Nothing more.
Sounds like along way to go, but even offering direct Skype chat via a client would be a welcomed addition to the homebrew community. The project is still in early stages, but we know people have been hacking away at sockets support in the community, so anything is possible.