Ok lets try to be more precise:
Im a taxi driver and the app is specific to get taxi runs from my radio-taxi service.
They asked me for the UDID code. I sent it.
They mailed me the app. A .ipa file about 9,9 Mb. I tried to unzip it and I'v seen the Payload folder with the app inside.
I doubleclicked the .ipa file and ITunes opened up. The icon for the app is now between the Iphone apps but the icon is the generic one and the genre too is generic.
Now I dont know how to put the app in the Iphone4 so I set the apps sync to manual and I'v to choose all the app that must be now copied to or deleted from the Iphone. I do this and include the Etaxi driver app.
I apply the changes and sync. The sync goes well for all the apps but when it comes to the Etaxi app theres a generic error message like "was not possible to intall the Etaxi app"
Maybe its not the way to install an .ipa file? Or something else?
Thx again