What do you mean? I'm pretty sure every app still works for the iPhone 4 except for Siri which can be added through jail breaking though. I have had no problem with older phones and android apps either
All my apps have worked on all my phones unless its blocked by the carrier or developer claims it won't work on a particular phone. Apps I bought in 2008 for my G1 still run on my Galaxy Nexus. But even the blocked apps can usually be side loaded some how.