How to download sms threader from computer to phone?

my brother just gave me his old sprint motorola q. i want to download an sms threader onto it because as of now, you have to go back and forth through sent and inbox to see a conversation, but i'm not used to this phone yet (have never had a smartphone) and dont know how to download an sms threader onto it. i do not have internet on the phone yet so i can't do it through the phone, can i download it onto my computer and put it on the phone? i have a usb connector. if so PLEASE include step by step instructions as i have no idea how to work this phone yet.