Phone in Panama -- compatibility w/ CR or Nicaragua?

Hi -- I'm from the States (cell phone = CDMA = no SIM card)

I bought two different local phones on my last trip through Costa Rica and Nicaragua.
(Apparently ICE in CR isn't compatible with Nicaragua's Claro.)

Does anyone know which one I should bring with me on my trip to Panama?
And is setting it up as easy as popping in a local SIM card?

Mucho thanks!