Older model iPhones are more popular than ever

The big number everyone’s going to be watching for during Apple’s(s AAPL) earnings announcement on Tuesday is how many iPhones it sold during its second fiscal quarter. We don’t know the total yet, but a study published by Consumer Intelligence Research Partners estimates how many of those were the latest model iPhone 5: about 53 percent of all iPhones sold worldwide.

It also found that the rest were iPhone 4 and iPhone 4S models, which sell for free with a contract or for $99 with a contract, respectively. That breakdown is slightly improved from December, when a CIRP survey shows that just half of all iPhones sold were the newest model iPhone 5.

CIRP January through March iPhone model purchases

CIRP January through March iPhone model purchases

This is a very different sales pattern than what we saw in the second quarter of the iPhone 4S’s availability. When that device was the latest model, it accounted for 73 percent of all iPhone sales in April 2012, a significantly larger share than the iPhone 5 had as of March, according to CIRP, whose data comes from a survey of 500 customers who’d recently bought an Apple device.

The iPhone 4S sold 33% of all iPhones in the survey period, while the iPhone 4 represented 14% of all iPhones. In contrast, in the similar period following the launch of the iPhone 4S, the lower-priced iPhone 4 represented 22% of sales, and the free iPhone 3GS represented 5% of sales.

As a share of iPhones sold, 33 percent is the highest share a legacy model iPhone has carried in at least the last two years, according to CIRP’s data. Apple wants to sell iPhones no matter what, but ideally it wants to sell more of the most expensive iPhones, not the severely discounted and free-on-contract devices; that way its average selling price stays high.

Something similar is taking place with iPads, CIRP found: Between January and March, the iPad 2 — which originally debuted in early 2011 — grabbed a larger share of iPad sales, up from 27 percent to 32 percent. The newest model, the iPad with Retina display, dropped from 43 percent of sales in the holiday quarter to 36 percent of sales during the January quarter. Meanwhile, the smaller and cheaper iPad mini grew slightly, from 30 percent to 32 percent of sales.

It’s not really a mystery that cheaper Apple devices, even when the devices are not the latest model, are attractive to buyers when viewed against the competition. What is a mystery (until tomorrow anyway) is how this affects Apple’s balance sheet.