Give back found phone or use it for my self?

I may or may not have found a phone on the side of the road. Then may or may not have taken said phone later to find an old friend calling the phone... Thus leading to me doing so researching and finding that this said phone belongs to the little sister of an old friend I have not seen in 3 years. Now time for you to help me solve this moral dilemma... Do I take the high road and sneak said phone into the mailbox of the rightful owners house... or the low road in witch I turn a profit???