The software is working with TCP connections and Serial Port connections to Siemens Hipath 3000 series PBXs. I have ported the software to be compatible with asterisk, therefore - when you write a CSTA application for one vendor, with minimal configuration changes, the software should work with another PBX. Some limitations/idiosyncrasies exist from PBX vendor to PBX vendor, so exactly the same results are not guaranteed without testing. At some stage, I'd hope to have a compatibility matrix available for developers and system integrators.