Add documentation for US and KR radios

Bug: 4445289
Change-Id: I6d91b56f9451a844fb1a35af6c82eddda0034a67
diff --git a/src/source/building-devices.md b/src/source/building-devices.md
index 7707962..fd7bed7 100644
--- a/src/source/building-devices.md
+++ b/src/source/building-devices.md
@@ -153,7 +153,7 @@
 However, no compatibility issues are expected when running newer systems
 with older bootloaders and radio images according to the following tables.
 
-Nexus S:
+Nexus S (worldwide version "XX"):
 
 Android Version | Preferred Bootloader | Preferred Radio | Also possible
 ----------------|----------------------|-----------------|--------------
@@ -161,6 +161,20 @@
 2.3.3           | I9020XXKA3           | I9020XXKB1      | All previous versions
 2.3.4           | I9020XXKA3           | I9020XXKD1      | All previous versions
 
+Nexus S (850MHz version "UC"):
+
+Android Version | Preferred Bootloader | Preferred Radio | Also possible
+----------------|----------------------|-----------------|--------------
+2.3.3           | I9020XXKA3           | I9020UCKB2
+2.3.4           | I9020XXKA3           | I9020UCKD1      | All previous versions
+
+Nexus S (Korea version "KR"):
+
+Android Version | Preferred Bootloader | Preferred Radio | Also possible
+----------------|----------------------|-----------------|--------------
+2.3.3           | I9020XXKA3           | I9020KRKB3
+2.3.4           | I9020XXKA3           | M200KRKC1       | All previous versions
+
 Nexus S 4G:
 
 Android Version | Preferred Bootloader | Preferred Radio | Also possible
@@ -170,6 +184,6 @@
 
 If you're building a new version of Android, if your Nexus S or Nexus S 4G has
 an older bootloader and radio image that is marked as being also possible in
-the table above but is not recognized by the build system, you can locally
+the table above but is not recognized by fastboot, you can locally
 delete the `version-bootloader` and `version-baseband` lines in
 `device/samsung/crespo/board-info.txt` or `device/samsung/crespo4g/board-info.txt`.