[brazzy]

Eventually they will buy software and services that provide value to them, which can be things for which first-world countries have an existing infrastructure, but which have so far been completely unavailable to these people.

For example, in parts of Africa, transferrable pre-paid phone credit has become a de facto bank acount for many people who've never had access to non-cash transactions.

Other examples: third-world countries have many subsistence farmers. Accurate local weather forecasts and information about current market prices in neighboring towns could be very valuable to them.

As for payment - credit cards may not play a huge role, but centralized app stores can easily support a diverse range of nation-specific payment options (like the phone credit mentioned above).