How to build a static library for both iPhone OS 3 and OS 4?

I created a .a lib file and it was built under iPhone OS 3.0 (in XCode 3.2.2). Now I found that it doesn't work on OS 4. I was using the lipo command to build the .a file for both simulator version and device version:

lipo -cre开发者_如何转开发ate libdevice.a libsimulator.a -output libcombined.a

Now I created another .a file under iPhone OS 4.0 (in XCode 3.2.3). My question is that is it possible to combine the two lib files together? (libcombined3.a and libcombined4.a)

the 4.0 version will work on 3.0, you don't need the 3.0 specific version anymore. Move completely over to iOS4.