Now those stories about Chinese housewives smuggling Apple (AAPL) iPhones onto the mainland make a little more sense.

It’s not just that the phones can be had in Hong Kong tax-free, it’s that they can be had at all.

Ticonderoga Securities’ Brian White, back from his recent China tour, reports in a note to clients Monday that the iPhone 4 is sold out for two months at Apple Stores, authorized resellers and China Unicom.

“In fact,” he writes, “we estimate China Unicom (CHU) has been unable to fulfill approximately one-third of the iPhone 4 orders due to shortages.”

Other findings:

• The high-end smartphone market in China is roughly 100 million to 125 million subscribers, which provides Apple, he says, “with a significant opportunity for growth in years ahead”
• China Mobile (CHL) confirmed to White that although it doesn’t sell iPhones, a special SIM card allows its subscribers to use them
• Total mobile subscribership in China grew 1.1% last month to 833 million, while 3G wireless ramped up nearly 10 times faster — up 10.4% in November to 31.6 million subscribers

“We continue to believe,” White concludes, “that China remains in the early stages of catching ‘Apple fever.'”

[Follow Philip Elmer-DeWitt on Twitter @philiped]