Disclaimer: This is all wild speculation on my part, I have no insider information.
Google has started adding support for GSM networks to Chrome OS on the Cr-48. As you may be aware, the Cr-48's Gobi 2000 3G Modem is capable of working on CDMA (Verizon/Sprint) and GSM networks (AT&T, T-mobile, and pretty much every other cellular network in the world). The Cr-48s that have shipped in the U.S. have only made use of CDMA, specifically Verizon's network. The GSM radio and that SIM card slot under the battery have sat unused so far.
Here's where the speculation begins. We think Google order 60,000 Cr-48s from Inventec. We think roughly a fourth of those, 15,000 laptops have shipped out in the 1st wave of deliveries. We know more Cr-48s are shipping very soon (though I wouldn't be surprised if they don't ship this week, shipping dates tend to slip). Might the 2nd wave of Cr-48s be an International launch? Or, with GSM support in it's infancy, maybe the plan is that the 3rd wave will be International?
While we wait to find out, feel free to throw out your own wild speculations in the comments :-)