Mobile carrier Claro, a subsidiary of América Móvil, will start offering the iPhone 5 on September 28 in Puerto Rico with some aggressive pricing. The iPhone 5 pricing will start at just $99 for the 16GB model. They did the same thing last year when they started offering the iPhone 4S.
This comes with a base plan of $64.98 a month, but with very limited data (see the chart below with iPhone 5 models and available plans).
Puerto Rico is a territory of the US, thus making Claro a US Regional carrier.
You can register online at Claro's website to get more information once the iPhone 5 arrives.