Q: My daughter inherited my old iPhone 4 after I upgraded to an iPhone 5. I bought her a separate instance of the TomTom app, but had her phone as another device on my account. We’ve created her own iCloud account and I’d like to transfer her TomTom app to her account/phone. How do I do that, please?
A: Unfortunately, you cannot transfer a purchased app from one iTunes Store account to another. However this may not actually be as necessary as you think.
Applications are associated with an iTunes Store account, rather than a specific device, and Apple’s policies in this regard are extremely flexible: You can have apps from a single account installed on as many devices as you “own or control”, and you can actually have apps from up to five different accounts installed on a single device.
So in other words you don’t necessarily need to actually transfer the purchased app to her iTunes Store account simply to leave it on her iPhone and allow her to continue using it. There’s no requirement for the user to be signed into a specific Apple ID in order to simply use applications; this is only necessarily to install them or update them using the on-device App Store. Alternatively, you can also simply transfer them on from your own iTunes library on your computer as part of a standard iTunes sync operation. The authorization to use the app is normally transferred along with the actual app.
Note that none of this has anything to do with the Apple ID that she uses for the iTunes Store, iCloud, or any other Apple service on her iPhone. Once the app is installed, she can continue using it normally regardless of which Apple IDs she uses to sign in to any other services on her device. The only exception is that she may need to use your Apple ID and password in order to download updates to an app when and if any do become available. If she lives close by, you could apply these updates for her from your own iTunes library or simply log in with your Apple ID and password on her device; however if this is a problem then it would definitely be a good idea to simply repurchase the app under her own account so that she could simply update it using her own Apple ID and password.
In terms of having “bought her a separate instance” of the app, it should be noted that it actually isn’t even possible to pay for the same app more than once from a given iTunes Store account; once you’ve purchased an app you can re-download it from your iTunes Store account as many times and to as many devices as you like without having to pay for it again. Attempting to “repurchase” an app with the same account that you originally purchased it with simply downloads your purchased copy to the current device.
In the case of TomTom, however, there are several versions available, and of course each one is treated as an entirely different app. If you owned TomTom U.S. & Canada, for example, and then purchased TomTom U.S.A. for your daughter’s iPhone, those would be two separate apps, and you would have paid for that second version in the same way as any other completely different app—probably needlessly so, for the reasons already noted above. Unless you did this, however, you didn’t actually purchase a “separate instance” for your daughter’s iPhone, but just downloaded the copy you already own onto her device.