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I purchased on my iPhone first. Then I went into my wife's phone and 'purchased' the traffic in-app, at which point I was told I'd already purchased and that I could download for free.

This didn't at all work for me.

My wife and I have separate iTunes accounts. However each of our computers is authorized with each others accounts and we have iTunes sharing set up between the two machines.

So, when my wife went to update Navigon it asked for my iTunes password for my account since that's what's associated with the application. I provided the password and Navigon updated on her iPhone successfully.

However, she cannot purchase traffic. When she clicks the buy button for traffic it comes up with an error saying you must first purchase this application in the iTunes store, then throws an error saying that the store cannot be reached.

I'm not sure if I can sign into my account on her phone long enough to put traffic on it or not, but the handling of the in application purchase when multiple devices are being used doesn't leave me very impressed.
 
Just an update.

So, I was able to log my wife out on her phone and log in my iTunes store account.

I then went into Navigon and purchased traffic. It said "you've already purchased this item" and enabled it on her device.

I then logged her account back into the phone and things seem to work.

If there are multiple accounts authorized on a computer to allow the playback of multiple account purchases then the same should hold on the mobile device.

i.e., if my wife's Mac is authorized for both her iTunes account and mine, then the phone should be authorized for both accounts also, to make things like in-app purchases work more smoothly.
 
I have 3 iPhones syncing to 1 iTunes account (one username/pw).

Adding traffic to two of those (a 3G and a 3Gs) iPhones worked with one purchase.
 
m3coolpix and acousticbiker, so when you add traffic to the 2nd iphone, it took you all the way to "confirm your in app purchase ... do you want to buy navigon traffic live for $19.99?", and then at that point you hit "yes" and it gave you a message that you have already purchased it and it is downloading for free and you are not being charged?
 
m3coolpix and acousticbiker, so when you add traffic to the 2nd iphone, it took you all the way to "confirm your in app purchase ... do you want to buy navigon traffic live for $19.99?", and then at that point you hit "yes" and it gave you a message that you have already purchased it and it is downloading for free and you are not being charged?

Yes. Even just checked my iTunes account history. It shows the original Navigon in app purchase three days ago for $19.99, and then another Navigon in app purchase today for $0.00.
 
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