According to one analyst, Apple has begun reducing iPhone orders, another indication that a sixth-generation model is looming on the horizon.

Based on checks with suppliers, Sterne Agee’s Shaw Wu wrote in a note to clients on Tuesday that Apple has drawn build plans for the current-gen iPhone models by up to 25 percent compared to the 35.1 million iPhones sold during the first quarter of this year.

As a result, Apple may ship no more than 28 million iPhones during the June quarter…

The figure would represent a healthy 40 percent year-over-year unit growth as the company sold 20.34 million iPhones during the June quarter of last year,  which was nearly four million more units than what analysts projected.

If Wu’s estimate holds true, investors won’t necessarily be pleased: Wall Street projected between 30-31 million iPhones for the June quarter.

Apple also has nearly nine million iPhones in channel inventory, enough for about 4-6 weeks. Wu expects the next iPhone during the September-October timeframe.

And according to AppleInsider, the analyst “has heard that Apple has increased build plans for its third-generation tablet”, adding that “Retina display availability has been addressed by adding an additional supplier, beyond Samsung”.

For iPhone sales to drop ahead of a new model introduction is nothing new. Typically, Apple experiences a pause and inventory drawdown a quarter or two ahead of a new model launch.

Love or hate it, but such is the nature of the smartphone business.

Apple typically refreshes its handset once a year, unlike other manufacturers that churn out new models on a monthly basis.

Other analysts are expressing concerns that a flurry of iPhone 5 rumors will affect iPhone sales leading up to the next iPhone launch.

This is also to be expected as would-be buyers withhold purchases in anticipation of the iPhone 5, or whatever Apple chooses to call it (our bet: “the new iPhone”).

What about you?

Have you already delayed your smartphone upgrade plans as the next iPhone looms?