when it appears in iTunes, restore it to factory defaults.
Go through the registration and now iTunes will know that his phone belongs to your account.
Purchased music should now install
Recently I switched from AT&T (iPhone 3s) to Verizon (Galaxy s3, hated it) Swapped a friend my galaxy s3 for his iPhone 4s and cash. My problem is I cannot sync the purchased apps to the iPhone 4s. How do I add the 4s to iTunes? thanks for any help.