1. Bitcoins can be spent directly for goods and services in their home countries, or
2. Bitcoins can be exchanged to the local currency at the cost lower than existing fiat-transfer fees. Note, even if this condition is met, there would be a huge imbalance in the direction of trade - coins coming into the country, not going out. To balance things out, arbitrage/fiat exchange is needed, with all the old cost we are trying to avoid here.
Option 1 is the only sustainable option in thr long term, and we are nowhere close to realizing it.
Actually I have sent money to the Philippines and the total price for converting from fiat to BTC and back to PHP is about the same or lower than the price Western Union charges.
HOWEVER: No offense, but these over-seas-workers aren't tech savy enough to use BTC. You guys ever been to the Philippines? Organization and education is.. lacking.