In a note to clients — as reported by “Fortune” ( — Katy Huberty drew on Morgan Stanley’s proprietary AlphaWise survey of buying patterns among China’s rapidly growing middle class. She says that, assuming 20% penetration, Apple should see, at a minimum, 24 million addition iPhone sales in 2013, adding US$6.50 per share to the company’s bottom line.

Among other things Huberty thinks:

° That there are roughly 150 million high-end subscribers in China currently paying at least RMB 100 ($16) per month for mobile phone service.

° China Unicom (CHU), currently Apple’s only official carrier, has 15 million of those subscribers, or roughly 10%.

° This year or early next, Apple will begin selling next-generation iPhones through China Mobile (120 million high-end subscribers) and China Telecom (15 million).

° Because 20% of China Unicom’s high-end subscribers buy iPhones, the other two carriers’ subscribers will follow suit. (8% China Mobile’s high-end customers already use iPhones, even though they get only 2G service.)

° As the iPhone catches on and the middle class expands, that number could grow to nearly 40 million next year, adding $10 to Apple’s earnings per share.

° The iPhone in China will reach penetration levels comparable to those of AT&T, where 63% of smartphone customers currently choose iPhones.

° In Morgan Stanley’s bull case scenario, Apple within a couple of years will be selling an additional 57 million iPhones per year in China alone.