You can't use itunes to transfer his music to the phone, but you can do it manually. The matrix supports a microSD card, so you would need one the size of his library at least. If you have a microSD card, I'll assume you have a card reader. Just go to My Music on the computer and there should be a folder called iTunes, and within that folder one called iTunes Music. Just copy the contents of that folder to the microSD card and then put it in the phone. He should now have his music on the phone.
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You can't use itunes to transfer his music to the phone, but you can do it manually. The matrix supports a microSD card, so you would need one the size of his library at least. If you have a microSD card, I'll assume you have a card reader. Just go to My Music on the computer and there should be a folder called iTunes, and within that folder one called iTunes Music. Just copy the contents of that folder to the microSD card and then put it in the phone. He should now have his music on the phone.