Have you thought about the structure of Android Contacts? How can you add your app into the Android Contact info page? Do, you know that there are 4 ways to write the same number in India? And you should better not try to call it from China... Why? Come to the presentation and let's talk about it!

And yes, saving all the numbers in e164 won't save you if you have millions of users in different countries and that users have different phones like Samsung, Oppo and Xiaomi...