Apple might launch only one of the two iPhones with larger screen this fall, according to UBS Analyst Steve Milunovich.

The Web site Barron's reported the investor's research note based on Milunovich's "checks" of the supply chain. The upcoming iPhone 6 has been heavily rumored to come in two sizes. Predictions pointed to 4.7- inch and 5.5-inch iPhones, up from the current 4-inch screen of iPhone 5s.

According to Milunovich's report, Apple works on those two models of iPhone 6 but the launch is still unsure.

"The stock may act better this summer in anticipation of new products... Our iPhone model is up just 10mn this year at 172mn vs 162mn last year... The second calendar half may surprise to the upside if either China Mobile or the iPhone 6 gain traction. Although the iPhone 6 could carry a lower margin since we would be surprised if it is priced at much of a premium, unit demand could be strong as surveys suggest Apple users want larger screen sizes."

He further added that, "... an "iPhone 6" is most likely to come in August or September, rather than June, in two different models, one with a 4.7-inch screen, one with a 5.5-inch screen. He thinks the former, the smaller of the two, "seems certain," but that the 5.5-inch model "may or may not launch at the same time and could be of the same resolution (lower pip), which would help app developers."

The analyst pegged iPhone 6 release will be in August or September. But the release date of the 5.5-inch model is less certain.

Another additional detail that the analyst cited was that the 5.5-inch iPhone 6 models will carry the same resolution as the 4.7-inch model. No much detail about the display resolution was mentioned.

There have been limited reports from Milunovich in the past. As such, it is difficult to ascertain the reliability of his predictions. iPhone 6 release date rumors are expected to accelerate as Apple gets closer to production.

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