I've read a bunch of stories about different parts of the world, especially in Africa, where people with mobile phones have started businesses by charging people a set, per-minute price to use their phones. Here in Colombia you can see this type of entrepreneurial business everywhere. What is different in these photos is that the phones are literally chained to the owner while the customers are using them.
I understand why this is the case. It would be relatively easy for someone to walk off with one of the phones while the owner is distracted with another customer but (to me) it looks kinda' funny. When I saw them I immediately thought about that executive-looking guy in the airport pacing back and forth while yelling into his phone and how frustrated he'd probably be by the chain.
The per-minute prices that I've seen are usually somewhere between 100 and 200 Pesos (approximately $0.05 to $0.10 U.S.) depending on where the owner is and how much competition is around. Both of these photos were taken in downtown Bogota within a couple of blocks of each other and their prices are both 150 per minute.
I've gotten to the point where I don't even need "minutes" in my mobile-phone plan anymore. 95% of my "phone" usage is data now and when I do need to make a call, I use Skype Mobile probably half the time. I'm sure that I'm not alone in this trend. Imagine you're out and you need to login to facebook to send that important message or unfriend someone special but that you're out of data in your contract. How long will it be before someone offers a price-per-kilobyte to people in the street? The sign might read "minuto 150 / kilobyte 02".