Apple doesn't release production data for its devices, but that hasn't stopped analysts from employing various work-around methods. Using historic sales data, which is made public and confirmed on a quarterly basis, assumptions can be made about inventory. Over at Asymco, analyst Horace Dediu has combined available data sets to build production ramps for a report entitled "Predicting iPhone Sales for Dummies."

"So here are the patterns of sales for the four versions of iPhone sold to date with some production ramps overlaid," Dediu wrote in introducing the graph displayed below. "The monthly sales are approximations based on actual quarterly sales divided over the months according to the number of days available."

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By keeping its products on similar production cycles, Apple has made it easy to see, using Dediu's data, that each new version of the iPhone has sold roughly double the previous version. Production starts out slow in the first month and ramps up quickly for five to seven months, before leveling off for another seven months or so. At that point, demand begins to drop -- perhaps a new version is released or rumors begin to circulate about the next software upgrade -- and production falls accordingly. Clearly, though, production falls a bit slower than it had ramped up the year before.

Using Dediu's charts and assumptions, 9to5Mac's Christian Zibreg predicts that Apple will sell about one hundred million units of the iPhone 5 before a sixth generation model is released. "In other words, a fifth-generation iPhone will match sales of all previous models combined," he wrote.

Zibreg's prediction sounds wild -- 100 million? -- but the numbers suggest it's a completely realistic goal. Worldwide demand for smartphones is expected to reach the 500 million mark at some point over the next two years, according to the Unofficial Apple Weblog. Moving 100 million units is necessary for Apple to maintain a comfortable 20 percent market share and, without any new competitors joining the fray or completely reimagined devices on the horizon, it should be doable.

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