How can I tell if a given *.ipa will run on an iPad or iPhone?
Every app has a info.plist file with some configurations for the app. Using this file, you could see if the app has been build for iPhone and iPod, or iPad. To view this file, do the following:


Make a backup of the .ipa file
Rename filename.ipa to filename.zip
Open the .zip file


In the zip file you just opened (or extracted), you have another app. With a right mouse click, you can show the package contents of that file.

When viewing the package content, there is an info.plist file. I prefer Xcode to view the data within the plist file, but on the App Store there're various other apps that your could download do view the contents of the plist file.

The info.plist file has a "UIDeviceFamily" key that should contain an array. The value of this array could be a 1 or 2 or both. Please refer to the image below to find out what the number means.