The folks at iFixIt found a dual-standard GSM/CDMA chip in the Verizon model of the iPhone 4: In Step 17, the teardown experts note that the Qualcomm MDM6600, which can support GSM standards up to HSPA+ (14.4 Mbps flavor) as well as Qualcomm's traditional CDMA voice and data standards up to EVDO Rev. A (deployed in the US by Verizon Wireless and Sprint Nextel) as well as EVDO Rev. B. There are an enormous number of shared characteristics between the GSM and CDMA standards, and Qualcomm represents a significant minority percentage of all the patents in a pool that's used for UMTS/HSPA.
Apple is spending more to put this dual-mode chip in, of course, than it would for a single-standard chip. But it makes a bloody lot of sense. By having a single chip that can be switched to GSM or CDMA, Apple can switch to a single line of manufacture to supply phones worldwide. They'll save the cost in a higher price for the chip by not having two separate products to make and track. I wouldn't be surprised if we see iPhone 4 models sold for the GSM market that are identical with new antenna locations to the so-called CDMA model.
Does this mean that Apple will offer a world phone for CDMA and GSM markets? Note that the Verizon version of the phone has no SIM slot nor built-in SIM card, so it can't be used on a GSM network in its current form even with a firmware update. Will an iPhone 5 be switchable? It's hard to tell. I imagine Verizon Wireless would prefer the CDMA lock in, but Verizon Wireless is minority-owned by Vodafone, a worldwide GSM provider, which would almost certainly like to sell a single model worldwide that could be easily switched to work in the US or in any of its non-US markets. There's a Droid that does that already.