Pay-by-the-minute phone booths?
When I was in Japan, I saw a handful of co-working style booths in a few subway stations that I believe you could rent with an app to take a call in. Something I've noticed about working in a cafe or otherwise public space is that there isn't a good place to take a call (video or phone). I try not to but can't help but be a little annoyed when there's someone in a coffee shop trying to take a video call in a public space.
Curious if there might be a market for launching these booths in public spaces, cafes, etc. where you'd charge by the minute (or some interval < 1 hr), and would open with an app/QR code, and have chargers/good lighting, A/C, etc. The idea is to offer people who are otherwise in public/working from a cafe/etc. a small amount of time to take an important call/have a quiet space in an otherwise loud or non-private environment. If you partnered with a cafe to install one you'd create some sort of revenue share model with the cafe.
I guess it will depend on the country/location.
You'd have to convince the cafe owner to give up precious real estate for your booth... not unless you'll be paying them a fixed monthly rent for use of the square footage space+utilities. And cafe owners want fast turnaround of customers, not encourage people to make their establishment a co-working space.
Maybe incubators, co-working spaces, startup spaces, hacker spaces will be a better fit for this? They can offer your service as a value added service on top of their usual plans.