Gammu and Wammu are free software projects which are done by volunteers in their free time. There is never enough of volunteers so you are very welcome to help us in any way. You really do not need developer skills to help.
Bellow is list of currently positions, which would be most helpful. If you won't find anything matching your skills, there still might be something where you can help, but was not found to be so important to be highlighted here. If you feel something could fit your skill, please contact us on mailing list.
We have quite comprehensive documentation, though there are still lot of places where it could be extended. You don't need any special skill for this, writing plain text is enough.
You have basic knowledge about Gammu and want to help others? Answering users questions or mailing list or IRC is the best you can do for them. Usually you don't need deep technical knowledge, most questions can be answered by looking at documentation.
Currently most of developers work on Linux or BSD. This leads to lacking support for Windows a bit. You probably need Visual Studio installed and you need some experiences with Windows API.
There are always things to translate to almost any language, just check dedicated page about translating.
Graphics and icons used in Wammu are quite poor quality right now. We would definitely make use of somebody more skilled in this area.
Gammu currently lacks support for Symbian. The only way how this can be covered is implementing application for Symbian, which we can use as communication end point to which we can talk (gnapplet is currently used for this purpose, but it lacks support for recent Symbian versions).
The very same probably applies to other modern platforms such as Android, Maemo or Windows Mobile.
Wammu could use much more attention from developers than it currently gets. You will have quite free hands to move project forward and make it look as you wish.
There is always lot of bugs and feature requests on Gammu core and more hands can manage them faster.