Shall or will?

When I learned English thirty plus years ago in China, we were taught to say "I shall", "we shall", and "you will", "he/she/it will". That is, "shall" for the first-person verb and "will" for the second- and third-person. But coming to the US, I realize "shall" is rarely said. It is said if the speaker intends to emphasize his (her) point and in that case it's not limited to the first person. I just came across the renowned English language linguist David Crystal's The Cambridge Encyclopedia of the English Language where (on p.224) he says "[m]odern usage does not observe this distinction. Indeed, it may never have existed in the language, but only in the minds of grammarians anxious to impose order on a 'messy' area of usage". Wasn't that enlightening, especially the latter statement! I don't know if the English textbooks in China still recommend that usage. It misled a generation of English learners back then. One coworker of mine who came to the US from southern China in the 1970s still says "I / we shall" today, though this is a fellow that couldn't care less about English, judging by his frequent spelling errors and strong accent in spite of his 40+ years living in the US. Fortunately, no other rules made up by the prescriptive grammarians came into the textbooks we were using, such as the no split infinitive rule (i.e. avoid saying "to fully understand"). Apparently the English educators in China did keep an eye on the actual usage of the language in English-speaking countries.