The POST binding is described in the official SOS specification and should be the default method.
The GET binding is described by OOTethys in a Best Practice document: https://web.archive.org/web/20120616065001/http://www.oostethys.org/best-practices/best-practices-get. It contains some special encoding for bounding boxes, as the only spatial filter, and time periods, as the only temporal filter.
The SOAP binding is not official with regards to the spec, and also not implemented yet.
The connection method can be changed on creation of a SOS
object.