I was looking for a word which was the opposite of "infrastructure", and playing the Latin root game instead found an obscure biology word. Ultrastructure refers to the fine-grained, minute cellular structures that comprise tissue and such; sort of infrastructure's infrastructure. Seemingly the opposite direction I was intending.
But the diversion allowed me to more carefully consider infrastructure. The other word I'm looking for is for the human (inter)action with the built infrastructure. The social scaffolding into which infrastructure is built and operates. The complement without which the infrastructure has no meaning. For now I'll call it "amphistructure", because this structure should have two sides, one which interacts with the infrastructure as necessary, and the other which interacts with the social structure. The amphistructure is the social abstraction layer, beneath which the activities performed are of no interest to the user. Interactions can happen on either side, or may require connections from one side to the other, and back again. I suspect that a circular model might be more appropriate, but I just don't see it yet.
And it may be that ultrastructure is what connects the amphistructure to both sides. The technical ultrastructure pictured above is what we interact with at a human level. Likewise, the social ultrastructure that Erving Goffman and other sociologists examine connects the other.
An interesting implication of this way of thinking are the points of contact between the structures. It allows for different conceptual analyses of socio-technical use. Rather than seeing the mobile phone as a tool through which social relations are (more or less) transparently carried out, we can see the phone as the ultrastructure connecting amphi- and infra-. The infra- then connects back to the amphistructure at a different location, creating a gateway to the sociostructure to complete the activity. The infrastructure thus expands the range and points of contacts available from within the amphistructure for all those interactions not available strictly on the sociostructure side of things.
Still sounds a bit muddled. Maybe diagramming it out will help. The ultrastructure seems to be where the interesting things happen.