Well, I don't want to step up for the local phone companies, but you have to take into account that Thailand has almost 100 million cellular lines (more lines than people in the country). The DR barely has around 11 million lines (also more than people). I work in the industry, and I know that the cost to serve 100 million users is much, much less than 10 times the cost serve 10 million. The more users you have, the cheaper it get to serve each one.
Furthermore, OP is complaining about the cost to call the country with possibly the most expensive rate (besides Cuba, that is) in the whole western world (Haiti). International carriers have to pay a lot of money to place a call to Haiti. With landlines it could be different, as they work on a different scheme. I don't know much about landlines, sorry.