install .ipa via iTunes on friends Mac I don't want to erase all my existing apps. I just want to install the .ipa file and KEEP all my existing apps. However iTunes says


  Are you sure you want to sync apps?
  All existing apps and their data on
  the iPhone "Simon Strandgaard's
  iPhone" will be replaced with apps
  from this iTunes library.


I really don't want to click the "Sync Apps" button.

I could go home and open iTunes on my own computer, but I'm at my friends place. How to do get the .ipa on my iPhone?
You can use the iPhone Configuration Utility to side-load apps onto an iOS device without 'syncing' and erasing your current content.

Config Utility for Mac
Config Utility for Windows

Keep in mind, though, that this will only work if the app is correctly codesigned and the device is correctly provisioned.