How many people are unlocking the iPhone for use on unauthorized wireless carriers? There's no exact way to tell, but numbers recently stated by AT&T in its quarterly earnings conference call are revealing.
AT&T says it ended 2007 with "just at or slightly under 2 million iPhone customers." Apple recently boasted that it had sold 4 million iPhones worldwide to date. Though the Apple's report didn't break down those sales by country (the iPhone sold, officially, in the US, UK, Germany, and France), it's safe to assume that the lion's share of activated phones came through AT&T: O2 has reportedly sold about 200,000 iPhones in the UK so far; figures from Germany and France, respectively, are likely lower.
At the risk of speculating wildly, let's ballpark the total number of iPhones that have been sold and activated through authorized carriers at 2.5 million. Allowing for lost/stolen/damaged replacements, prepaid plans (we're not sure whether or not they're counted in carrier figures), etc., that leaves a huge group of devices open to potential unlocking.
In fact, since Apple derives revenue from carrier subscription fees, the company has accounted for unlocking as a significant financial concern in its recent 2007 10-K filing:
"Because the Company's agreements require each carrier to make revenue-generating payments to the Company, a carrier?s non-performance under or termination of an agreement, or its inability to attract and retain iPhone customers, could have a material adverse effect on the Company's future financial condition and operating results. If, contrary to the Company's license agreements or product specifications, an iPhone is "unlocked" from an authorized carrier?s network, the Company would not receive payments related to that iPhone from such carrier, which could have a material adverse effect on the Company's future financial condition and operating results. The Company may choose to enter into arrangements with carriers in other countries or regions, and the same risks described above would also apply to those arrangements."
Apple continues to instigate mechanisms for preventing unlocks in successive software/firmware updates for the iPhone. The latest 1.1.3 release has, thus far, proven impervious to previous unlock methods.