I have just submit my app to the App store, and received many comments that the application crashes on startup on older iphones. The deployment target was set to 3.1.3 and base sdk to 4.0. I thought I didn't use any api from 4.0 so the only problem could be three20 library.
Now I have two xcodes installed on my computer. After some changes my project can be build both in the newest one (3.2.3), and in the 3.2.1 with the base sdk set to 3.1.3 and deployment target to 3.0. My app works in iphone simulator in both xcodes and all versions (ranging from 3.0 to 4.0).
Now my question - if my project can be built with base sdk set to 3.1.3, will it run on the real device if I build it with 4.0 and choose deployment target to 3.0? I have only access to real device with iOS 4.0 and no other way to check whether everything is ok.
with the 4.0 sdk you can set the deployment target to 3.0 and the base sdk to 4.0 and it should be fine. If you have the old simulator installed still you could then run this build (don't rebuild from the 3.1.3 base sdk!) on the simulator to test it there, although having an old device would be ideal.