unlock

Did you buy it outright or with a contract?
Edit: I see you have the Samsung S6 from your info page

 

You could try to Google your question. You could also search a video on YouTube stating how to unlock a Sprint phone in the search box. Hope this help's!!!

 

Ah, so your boyfriend bought the device from someone who now is unreachable to inquire about the device still being under contract correct?
Well, I would suggest asking Sprint how to go about getting the device free and clear of them, so that Sprint can issue you an unlock code.
From my understanding, devices under contract for "X" amount of time cannot be unlocked legally.
I will stand corrected if someone can provide some clarification on that

She probably did Google that question and landed her here, hence the question

 

Yeah, that pretty much sums up the matter:
http://arstechnica.com/business/2015/02/starting-today-wireless-carriers-have-to-unlock-your-phone/

This could be a pretty messy thing to clear up. Since the phone's original owner can't be contacted, even if you provide documented proof it was a valid purchase as far as Sprint is concerned it's under no obligation to unlock it because there's still an open account. Also, Sprint phones are a CDMA based, there's no SIM card like with GSM phones so Sprint pretty much holds all the cards in this game until that open account gets closed.
https://www.puretalkusa.com/blog/whats-the-deal-with-unlocked-phones/