How does syncing apps with more than one iPhones work?

Question

Me and my girlfriend both has a iPhone. I was wondering do I have to purchase the app twice for both iPhones?are apps tied with my computer, the phone or my iTunes account? Assuming I purchase it from my mac there's no way to say which iPhone it is for so I assume I can use of on both phone? But what of I bought it from the phone?

Answer 1

Yes you can do this. It works just like music, you do not have to purchase an app twice if, for example, you purchase an app and then would like to also put it onto your husband or wife's iPhone. You can authorize up to five computers to "hold onto" the app and allow it to be synchronized down to the iPhone. I did this with two computers, mine and my wife's, synching to two iPhones, mine and hers. There's probably a limit of 5 iPhones too, but I don't know for sure.
You can simply email an app, or put it onto a CD or external storage device to move it to another computer, and then authorize it on the additional computer.
Here's what you need to know:
Go to iTunes on a computer that has the app. Top left, Library menu, click on Applications to display the applications which are on this computer. You'll get a big screen that says IPhone and IPod Touch Apps, and icons for each. Right click (Control-click if you have to) to get the contextual menu, and select "Show in Finder." All of your apps should be residing in the resulting folder. Grab one or more of them and email or copy to a CD or external drive (or transfer by network) to get the app onto the additional computer. On my computer this is the "Mobile Applications" folder in my iTunes Library; this appears to be the default location. Of course you need to put the app into the correct default folder on the new computer.
Once the app(s) is on the new computer, it may not show up in iTunes (look in the same place; in other words, open iTunes, go to "Library --> Applications" top left). If it's not showing up in iTunes, then simply go back to the folder (the actual app in the finder) and right-click and select Open With --> iTunes. That'll force it to show up. Your goal is for the app to show up in iTunes on the "new" (additional) computer. Once it shows up, you are almost there, although it is not yet authorized, so if you go ahead and sync with your iPhone on this additional computer the transfer will fail.
To authorize it, simply double click on the app IN iTUNES, right there in the Library -->Applications view. A window will pop up and say you are not authorized to play this (just like it does when you try to play a song you originally purchased on a different computer). The user name that is displayed will be the user name of the original purchaser. Enter the password of the original purchaser. You are good to go. If you added multiple apps, they will all become authorized on this additional computer with this single authorization action, you do not have to repeat the authorization for each of them, as long as they all were purchased by the same user.
Proceed with syncing the additional iPhone using iTunes on the additonal computer. You are done. Enjoy!
This will work with no regard to AT+T accounts, it's not related to them at all. You can have five authorized computers, including the one which originally purchased the song or app. You can send an app to a friend who lives in a faraway place and allow him to authorize his computer to play your apps and songs. Note that he will be able to play all of your apps and songs forever until you deauthorize his computer. This does not mean he will have access to your account in any way; simply that he will have general authorization for any songs or apps you send him; he won't need to re-authorize any new things you send him. In order to allow you to maintain control (change your mind) there is an option in the iTunes Store (Account button) which allows you to deauthorize ALL computers on your account, if you wish to reauthorize individual computers again.
The apps and songs are simply password protected. If you send one to someone they won't be able to use it unless they know your password, and you can allow this up to five times (for five computers).