Nice job with that beta test. You're right that for a developer to send you a pre-release copy of an iOS application (in other words, one for the iPhone or iPad), they need to know the unique IMEI (which stands for "International Mobile Equipment Identity" btw) number so they can "bake in" what phones can run the application.

Problem is, it's not something that's obvious or easy to find in iTunes or on the phone itself. Well, actually, if you go to Settings --> General --> About and scroll down, you'll find that the iPhone / iPad will show you the IMEI and the ICCID (stands for "Integrated Circuit Card Identification", it's the serial number of the SIM card in your phone), which you could just take a screen shot of and email to the developers, but let's see how to find this information in iTunes instead.

The trick is to know that the information is in iTunes but that it's rather a hidden feature, not staring you in the face.

Plug in your iPhone to your computer and you'll see a display that shows all sorts of information about your device, like this:

(I've obscured some of this information to protect my own device and to avoid confusion, but I'm sure you can compare what I am showing with what you have and figure things out!)

Here's where it gets interesting. Click on your phone number...

Cool. There's that IMEI number! Now, click on it again...

Sure enough, it also shows you the ICCID number right there in iTunes too.

Let me show you something even more interesting: iTunes stores the IMEI and ICCID of every device you've ever sync'd with iTunes, including previous generation iPhones if you, like me, keep upgrading and switching them out.

To find that information, go to Preferences... off the iTunes menu on the top left and click on 'Devices':

It shows you a list of every device you've ever sync'd with this copy of iTunes:

Now move the cursor over one of the backups and let it sit there for a second or two:

When it's an iOS cellphone device, it shows you the IMEI and ICCID value. Nifty, eh? A quick screen capture of that pop-up and you can just email it to the developer and Bob's your Uncle!