Since I have an external application that needs to work with ISPConfig and it is written in C++ and SOAP is pretty outdated and ugly in regards to transportability, I have written a JSON/JSONP wrapper for the ISPConfig 3 Remote API. You can find it at https://bitbucket.org/bolvarak/ispconfig-json-wrapper. Thanks and enjoy!
Thank you for making your wrapper available. The ispconfig master branch (3.1 release) has already a jsown (REST) api available beside the soap api.