I honestly cannot tell what you are asking. You just posted an entire paragraph of word salad with zero punctuation. You "don't want to send a friend again." You want to " / one galaxy to another."
If it's an "unlocked clean Galaxy that was my AT&T" what does Sprint have to do with it? It's an unlocked phone, there is nothing else for Sprint to do unless it's blacklisted. Assuming that it is an unlocked phone, which is what you seemed to say, and it can run on a GSM network (Sprint uses a CDMA network, while AT&T uses GSM), what's the problem?