Unlike Apple (AAPL), which reports on a quarterly basis how many iPhones it has shipped, AT&T keeps its unit sales figures close to its chest.

The new memo trumpets the fact that iPhone sales on June 19 “exceeded sales recorded on 2008’s iPhone launch day,” without saying how many phones it sold on either day.

But by extrapolating from previous quarters and reading between the lines, we can make some rough estimates. Here are the data points as we understand them:

• June 29 and 30: Apple launches first iPhone, and AT&T and Apple together sell 270,000 units in two days.  In its Q2 earnings call the next month, AT&T CFO Rick Lindner says his company activated 146,000 iPhones in the last day and a half of the quarter.
• Oct. 2007: Apple announces that it has sold a total 1.39 million iPhones; AT&T says it has activated 1.1 million of them.
• Jan. 2008: Apple says it has sold 4 million iPhones; AT&T says it has activated about 2 million (sparking much hand-wringing about the “missing” 2 million iPhones)
• July 11, 2008: Apple sells more than 1 million iPhone 3Gs in 21 countries over the space of three days. AT&T later says its stores sold nearly twice as many iPhones that weekend as they did the weekend of the first iPhone launch. Even if AT&T’s sales equaled Apple’s, that can’t be more than 270,000.
• Oct. 2008: Apple announces that it sold 6.9 million iPhones in its September quarter. AT&T says it activated 2.4 million of them, about 35%. (Overseas sales and unlocked iPhones presumably making up most of the difference.)
• Jan. 2009: AT&T says it activated more than 4 million iPhone 3Gs in the previous six months. In that period, Apple had sold 11.25 million iPhones. Again, AT&T’s activations represent about 35% of the total.
• June 2009: Apple launches the 3GS and again sells more than 1 million iPhones in the space of three days, but this time in only 8 countries, not 21.
• July 2: AT&T’s memo says it sold more iPhones over the June 19 weekend than it did over the July 11, 2008 weekend. That makes sense, given that the U.S. (and thus AT&T) share of Apple’s sales was larger this year.

Assuming the 35% ratio holds up, it’s not unlikely that AT&T will eventually activate about 350,000 of the new iPhones sold the weekend of June 19 — many of them Apple Stores — and that actually unit sales at AT&T outlets that weekend could easily exceed 300,000.

AT&T’s public relations department announced that it sold “hundreds of thousands” through its pre-order process prior to launch, and would say no more.

Photo courtesy of AppleInsider.

Below the fold: The iPhone portion of the AT&T memo, as leaked to MacDailyNews.

“iLaunch day 2009 was one for the record books, as AT∓T customers scrambled to get their hands on the fastest, most powerful iPhone yet.

Here’s a look at some of the milestones we achieved:

• Best-ever sales day in our retail stores
• Second-largest traffic day in our retail stores
• Most transactions processed via our IT systems in a single day
• Most upgrade eligibility checks in a single day
• Largest order day in att.com history
• Largest features sales day in att.com history

On this year’s launch day, iPhone sales exceeded sales recorded on 2008’s iPhone launch day, Black Friday 2008 and Dec. 26, 2008 — all heavy-volume sales days. In fact, this year we surpassed 2008’s launch day sales at about noon Central time, and sustained our previous peak hour record, also set in 2008, for 11 straight hours.” (link)