Google had a lovely related article recently of data centers built around many old stripped down phones. The main focus seems to be a university experiment,

> Researchers at the University of California San Diego are planning a 2,000-phone computing cluster to support computer science classes such as Parallel Computation and Systems Programming. Early experiments show that even a moderately-sized cluster of 20 phones is capable of supporting peak submission rates for a 75+ student class, with grading latencies below the default AWS backend. A 2,000 phone deployment will be capable of supporting a hundred such classes at once.

https://research.google/blog/a-low-carbon-computing-platform... https://news.ycombinator.com/item?id=48515336

I do think there is huge potential here for things like running lots of semi persistent agent harnesses. The work time is currently massively dominated by the remote LLMs, so running on old phones would be cheap and because of Amdahl's Law it wouldnt really be much slower.