This link http://android.wordpress.org/2010/05/11/wordpress-for-android-version-1-2-geotagging-and-video-upload/ has the secret sauce for uploading 3gp videos to a wordpress blog namely the PJW Mime Config plugin.
After installing PJW Mime Config the mime type you need to add under Settings ==> Mime Types using the PJW Mime Config plugin is:
File Extension: 3gp
Associated mime-type: video/3gpp
Of course without the functionality of the Videopress plugin which enables conversion of 3gp into multiple formats you will only have 3gp video’s available on your self hosted blog.