To answer the question for you guys over the pond a sim free phone doesn't do much for you except for the travel benefits.
However over here in the uk going sim free allows for better carrier deals.
Sim free for me makes my 30 day rolling contract £18.90 for unlimited data (6gb tethering), unlimited texts and 600 minutes of calls.
To get the same deal with the phone would be £65 plus £99 upfront on a 24 month contacts.