Upgrade Cycle for the Galaxy S IV
Samsung seems to be set on introducing a new Galaxy S every year in the late spring or early summer.
This makes early April the best time to sell your old Samsung Galaxy S4. Of course, your time table
to sell may depend on where you are in your carrier contract. Used phones almost never go up in value.
So to get the most money for your Samsung Galaxy S4, sell it as soon as you have your new one activated.