Since you returned the phone, you won't be arrested.If you had NOT returned the phone but knew who owned it, you could be charged with larceny.  Larceny is theft.  Larceny is the trespassory taking and carrying away of the personal property of another with the intent to permanently deprive. If you had taken the phone and not returned it when you knew who owned it, you would have intended to permanently deprive the owner of his personal property and could be charged with larceny.If you had taken the phone and knew who owned it, the rightful owner could have sued you for conversion.  Conversion is the unauthorized assumption and exercise of the right of ownership over the personal property of another to the exclusion of the owner's rights.  Conversion is any unauthorized act which deprives an owner of his property permanently or for an indefinite time.