LMAO. He says Mid range and you say S3. Oh Pnizzle.
I'm seeing Metro S3 users are slowly turning into 2008 Apple Iphone users. Sad
OP, If the esteem was to get the correct radio firmware flashed over, It could POSSIBLY be used with a SIM card on metro but its doubtful.
I know you said you wanted to switch to Metro but consider your options. I would buy a compatible GSM phone and run it on Tmob's "Bring your own device" plan. They have several option to choose from for a plan and they range from $40 to $60. Great plan options, no contract, use whatever phone you want and you get MUCH MUCH MUCH faster data speeds than Metro. Plus you can walk away if you dont like it and go to straight talk, simple mobile, etc...
I was getting 1.3Mbps 4Glte on Metro with my Esteem. I know get 7-10Mbps with my GNex on Straight Talk. Sure LTE is great but what good is it when your running at 1.3Mbps? People have this misconception of LTE thinking that it's somehow better. Data speeds are data speeds, 5mbps is 5mbps no matter what radio your on. LTE can achieve MUCH higher speeds which is what makes it great. Downside is battery life. Trade off isnt worth it. Still pointless on metro when you barely scratch the surface of what REAL LTE users are getting on Verizon. Plus LTE is the worst battery killer of them all. HSPA gets better speeds than Metro plus you save 2-3 times the battery life. Google is selling the Gnex straight from the Play store for $349. Not sure what your wanting to spend but you cant beat that price for what your getting. The Nexus is still the #1 developer phone from which hardware specs are only slightly different than the S3. Plus the Nexus 4 is coming out in a few days so the price will prolly drop even more OR you can get the Nexus 4. Regardless, you can pick whatever phone you want as long as it is GSM.
Metro is still great. I was a user for 5 years. But now that I grew some balls and actually walked away, I've seen the light and I've seen that I can get MUCH MUCH MUCH better for the same price. PLUS, I can get whatever phone I want that wont be limited to just Metro's network.
Hope this helps.