You don't have to own an iPhone/iPad. You can borrow one just fine.

Also, they have an iPhone and iPad simulator that you can launch and test with from Xcode, so you can do most of your testing on your simulator if you want and then test on your friend's phone when you need.

You do need a Mac though, as Apple's iOS developer tools are only built for OS X, so you can't build an iOS app on Windows or Linux. If you're using a 3rd party "cross-platform" development tool/library (like Unity or Mono or Phonegap, for example), I'm not sure if they let you build "on the cloud" and don't require you to build yourself on a Mac. I think I recall at least one such tool/library existing, but I don't remember what.

Also, yes, when you register for the 99$ developer program, you do it with your Apple account, and it is linked to your account; but they don't link your phone/device to your account for testing. You can test on any device just fine.

Thanks for your answers ! So I can borrow it. cool.

As for the mac, I'm creating an app in AS3 (with Adobe Flash Pro), so I suppose that I'll just have to send to the app store the .app file. no ? (it's not as simple as Android ?)

Its not that simple. There are a lot more steps to get an app on the ios store.

Thanks for your answers ! So I can borrow it. cool.

As for the mac, I'm creating an app in AS3 (with Adobe Flash Pro), so I suppose that I'll just have to send to the app store the .app file. no ? (it's not as simple as Android ?)

Nope, it's definitely not that simple. Apple reviews every app submitted, and it is quite common for them to reject apps. After they reject the app, you have to make the necessary changes to comply with their rules, and then resubmit.

I'm assuming you'll use Adobe Air to get your application to run on iOS. iOS does not use the same .app structure that OS X does. It uses .ipa, which you create using the iOS developer tools. I'm not familiar with Adobe Air, though, so I don't know the actual process.

Sorry, last question, if I borrow an Iphone, what's the procedure to import my app in the device ? (as the device is not linked to my apple account)

Plug the device in to your computer, open iTunes, and install the .ipa to the device (you can do this from Windows or OS X, so long as you have the .ipa you want to install). Note that if you do this, and if your app is not on the App Store, you have to embed the iDevice's UUID/UDID into the app to enable it (or else iOS's security will refuse to run the app, as it's not been approved/signed by the App Store).

I'm not sure how using Flash works, but normally you'd be developing in Xcode and be able to launch the app on the iDevice straight from Xcode (assuming it's connected to the computer). That way you can actually debug the app.

Honestly though, if you're serious about this, go buy a Mac (you can get a Mac Mini for $600; cheaper if you get a used/refurbished one) and an iPod Touch (cheaper than an iPhone, but same development process). You're in for a world of pain if you don't have access to Apple devices and yet are trying to make an app for Apple devices. This is actually why I own a MacBook Pro. Last year I got a new job with Pixio, and we specialize in making iOS and Android apps. Despite the fact that I am mostly on our Android team, I do occasional iOS work too and needed a Mac to allow me to do iOS work. Without it, it's just not very practical to develop for iOS.