Seda is correct, the ringtones and ringback tones are assigned to the phone that was logged in at the time of purchase. If you intended to purchase them for YOUR number, and NOT your wife's, then you need to create an account for your line and purchase with that account. You may be able to call Customer Service and explain, and they can probably switch the ringback tones to your phone without a problem. If the ringtone has already been sent and downloaded to your wife's phone, then it will need to be repurchased for your phone.
HTH,