That's One Ringy-Dingy:payphones & the market for coins

What do you do if you want to make a long distance call in Saudi Arabia? Obtaining phone service is very difficult. That leaves pay phones and phone cabins. But the pay phones require the use of obsolete coins.

Surprise! There is a market for the older coins!

The problem ... was that payphones would only take 'old' ten-halala coins. A smaller version of this coin had been introduced previously, but STC had never got around to converting their payphones to use it, so you had to find the obsolete version of the coin if you wanted to make an international call. Well, these coins were no longer in general circulation, because some canny old men had spotted a niche market and were exploiting it ruthlessly. They would somehow manage to collect all available old 10 halala coins, and they would hang around clusters of phone booths and sell a bag of nine coins for ten riyals.

[h/t to The Emirates Economist]

Is there a black market for pre-paid cell phones with UAE service in Saudi Arabia?