Do i need to turn my phone in?

Okay so we upgraded over from Sprint to T-Mobile. We were told we could port our numbers right there in store (which we did) and she told us it would automatically cancel the plan at sprint. My wife was the only one who had it done since my phone had to ship to the store. When we went online on Sprint, only my number was listed and her's was not (which makes sense if it was removed while changing carriers) My question is, do I have to physically turn my phones in back to sprint even though we're way past the 2 year lease and are now on a month to month flex lease, or am I able to keep the phones? Every time we would change carriers when I was younger or even upgraded, I never had to give up my previous phone.