That was my first thought when I got unlimited mobile data back in ~2006. I could be always on IRC, seed torrents infinitely... and that's when the teenage lucb1e realized that there is no port forwarding on mobile networks and why that is a problem.

To this day I wonder why nobody seems to care at all about that. It's like being on the real internet except you can't reach each other, you have to always go through some third party that is on the internet proper.

At least we got "net neutrality" now, which doesn't apply to SYN packets for some reason but at least it applies in the other direction, so no more 'blocked site' page on buienradar.mobi because KPN wanted to sell its expensive SMS weather service instead of this newly popular weather radar site.

For what it's worth, I did compile and run a bitcoin miner on my phone ten years ago. Running services on it isn't exactly a new idea, but now that they're so powerful, it also means we can't supply enough power from the battery or dissipate enough heat while in a pocket.