Default Need help getting my Sprint Galaxy S3 onto Virgin Mobile

Like the title says. My previous Phone bill from Sprint was too much for me so I decided to cancel. I'm now with Virgin Mobile because of their cheaper plans and I know they use the Galaxy S3 so I was wondering. How can I start using my Galaxy S3 with them? I have a clean IMEI & the Phone is free of any hidden charges. Can somebody help me please. I'm not the best when it comes to these kinds of things...

Any help is appreciated