Communications Alliance creates Industry Codes that define good industry practice. In many cases these Codes are enforceable by the Australian government regulators
Guidelines are documents with which compliance is voluntary (although they may be enforceable through reference to the Guideline in a contract or through adoption by a regulator). They cover a range of industry topics including consumer, operational and technical matters.
Standards cover a range of technical topics. Most of them define the technical parameters of "Customer Equipment" e.g. phones, modems, PBXs.
Specifications are usually voluntary documents that are technical in nature. They are mainly used for the connecting together of telecommunications networks.