I’m actually really surprised that males / females are born at close to 50 / 50.
A population in which births are overwhelmingly female means those who give birth to males have an advantage in passing down their genetic material. In your scenario a man will likely have more descendants than a woman, so genes that arise promoting male children would be favored. If you reverse the ratio and the population is overwhelmingly male then being female gives you an advantage and genes promoting female children would become favored. So you get a tug of war that balances out at roughly 50/50. This is known as Fischer's principle.
Given the state of data harvesting I imagine purchasing a list of phone numbers associated with a given demographic is trivial.