Image by Toban Black
These ads are in a lot of phone booths in the UK.
If I’m not mistaken, the ads generally sell sex workers (who most people would describe as "prostitutes".) (I also noticed ads that offered massages; but given the other stickers they’re pasted up with, I have doubts about whether those ads truly are just about massages.)
There is a lot of nudity on the ads.
Some people refer to the ads as "call cards."
(I haven’t read most of those articles, myself.)
This 2008 photo displays some of those call cards –