Hooray! It looks like Google, Samsung, and Sprint were able to iron out the difficulties in redistributing the closed source radio code for the Nexus S 4G and it's now officially a part of the AOSP (Android Open Source Project) again! Says Jean-Baptiste Queru, Technical Lead, Android Open Source Project --
We've been able to resolve the issues around Nexus S 4G, and we can now properly distribute its CDMA and WiMAX binaries. That allows Nexus S 4G to work with AOSP just as well as Nexus S.
As a result, we now consider Nexus S 4G to be fully supported in AOSP,with no restrictions. Overall, Nexus S is the preferred platform for AOSP work.
I've updated the set of IMM76L binaries for Nexus S 4G to include WiMAX support. They're available at their usual location: https://developers.google.com/android/nexus/drivers
Enjoy we will. Welcome back to the family, Nexus S 4G. We've missed you. You might remember back in February, support for CDMA devices was dropped from the AOSP. Dan Morrill explained that this was because binaries for proprietary radio code was signed by a different private key, and projects built from the AOSP would use the standard platform key. This would lead to all sorts of difficulties, and official support for the devices had to be dropped. Legal issues tend to conflict with open-source more often than not. It seems that the issues have been resolved, and Google can now deliver binaries with the correct key, and the Crespo 4G is alive and kicking in AOSP.
It's worth noting that there's no mention of the Sprint Galaxy Nexus, which uses LTE for the 4G network in place of WiMax. Hopefully, those issues can be resolved as well and we're one big happy Nexus family again.
Source: Android Building Group