P2P international calling with ElyNet is practically free, and the best part is, your home cell phone number never changes!
are you planning a bounty campaign?
Is there an explanation why they want to implement their business in Cambodia and Uzbekistan first rather than in South Korea?

It is a South Korean Telecom company. I am expecting they will be launching in South Korea first?
There are already apps that you can use free for international calls.
What would be the major selling factor of this platform?
Calls? It's not for calls; it's for data. You get data packages at a flat fee irrespective of travel, and the selling factor is also that the data prices are well below the norm found in many countries.
As for operations, Union Mobile is already the fourth largest mobile company in South Korea. However, the mobile sector is highly regulated in each country. Releasing a new blockchain network for mobile data will require important legal nodes, which have been cleared with the two countries you mentioned.