The major takeaways of this work are:

(1) For specific workloads, clusters of repurposed phones are cheaper and more carbon efficient than traditional servers.

(2) More broadly, scavenging unwanted equipment shows excellent potential for building economic and carbon-efficient systems, especially when renewable energy is plentiful.

(3) Sustainability has operational and manufacturing facets; manufacturing dominates as operating trends towards zero with cleaner energy mixes.

(4) Accurate LCA information is essential for carbon-based analyses; it would be beneficial if more ICT manufacturers published this information, including cloud providers who build custom systems. Our work highlights the need for more holistic analyses of the environmental impact of computing. With the substantial carbon cost of manufacturing and the difficulties of responsible recycling, the energy efficiency of a device may be the least significant component of its environmental and human impact.