In creating the IPA you would have used a provisioning profile. If that is a development one, or a distribution ad hoc one, you will have chosen what devices the IPA is allowed to work on.
So, make a distribution ad hoc profile that includes all of the devices on your iPhone developer account, and make the IPA using that profile. Now when you have made the IPA you can give it to the people who own those devices.
If they are all your own devices (or people who you see each day) you could connect each one to your Mac, and use Xcode's Organizer or Devices window (depending on which version of Xcode you use) and drag the IPA into the Applications list for the device.
If the devices are owned by other people you don't get to see, you can either send the IPA to them and they would use iTunes to get it onto their device, or if you can post the IPA online you can send a link to them, and they can install the IPA directly from the web page.
The web server will have to be HTTPS, you can't use HTTP services since iOS 7.1 came out. To post the IPA online you can use this utility: