Some interesting observations from Asymco’s Horace Dediu who used data published by Deutsche Bank and the ITU to put into perspective the world’s pre-paid users who buy contract-free $700-$1000 handsets for use with pay-as-you-go plans against post-paid subscribers who get the latest and greatest devices subsidized for up to $200 provided they pledge to a lengthy 12-24 months wireless contract:

Roughly 1.5 billion are post-paid and 3.7 billion are pre-paid. That means that nearly 70% of the world is not being addressed by the iPhone as it currently stands. Put another way, a shift in positioning might result in a 250% increase in addressable market.

The regional breakdown tells a similar story (below). Apple will eventually fill 100 percent of key post-paid (blue areas) addressable markets through the virtue of the expansion of carrier agreements. For example, half the US and Canada area being finally filled in this year. What about pre-paid orange areas?

There’s little doubt that Apple is thinking about – if not already working on – branching out the iPhone into the 3.7 billion people pre-paid markets with an inexpensive iPhone model, if not an entirely new product to cater for the segment (iPhone nano, anyone?). Some analysts already see two iPhones in late September, one for pre-paid and the other for post-paid customers. The lucrative high-end segment will eventually dry up so Apple will have to turn its attention towards mid- and low-range segments. iPhone is either victorious in markets like Australia or battling Google for the #1 spot and with RIM developers attracted to the platform Apple clearly has the momentum.

Daring Fireball’s John Gruber sums it up nicely:

Examine the history of the iPod to see how this will play out. They’ll press technologically at the high end, and they’ll expand into the mid-range market with lower priced models. Why not now?