Because the Simulator 3.2 and 4.0 in the SDK 4 do NOT actually work for iPhone simulation (which always comes out iPad and not responding at all), I ended up with 2 SDK installations, using SDK 3.1.3/Simulator 3.1 for simulation, and SDK 4 for building onto the iPhone with OS 4. (More details here.)
I tried to use the old Simulator 3.1 from the SDK4-XCode 3.2.3, e.g. by copying the full "iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator3.1.3.sdk" directory into the corresponding XCode3.2.3 directory, and choose the Simulator-3.1.3 (which does appear in the "Active Executable" list), but it cannot build, with more than 30 errors, e.g.
Undefined symbols:
"_OBJC_CLASS_$_NSURLConnection", referenced from: objc-class-ref-to-NSURLConnection in GRACEViewController.o
"_OBJC_CLASS_$_NSString", referenced from: objc-class-ref-to-NSString in GRACEViewController.o
Is there a way to use Simulator 3.1 (instead of Simulator 3.2 or 4.0) when using XCode 3.2.3 (which is a must to build into iPhones on OS 4) ???