So right now i have sprint and my dad pays for my phone. I have 2 phones a galaxy s5 and a galaxy s7 edge. Right now my service is on my s5 but i can change/activate a new phone and switch the service over at anytime. If i switch the service onto the galaxy s7 and take the sim card out of the s5 meaning it won't and have any service at all and buy a prepaid service will i be able to use the s5 or do i have to unlock it? I also legally own both phones.