It really depends on a number of things. What kind of soldering are you doing on the logic board? Because of how small and squeezed together the components on the iPhone's logic board are, I would say your first priority once you get a soldering iron should be to find a very fine tip for it.

As for the different stations, I can provide some insight. I have used our economy soldering station as well as the Weller unit we use in our lab. I have successfully performed surface-mount soldering and de-soldering with the economy unit to refurbish Nintendo Wii DVD drives with no problems. It definitely does its job, but the higher quality unit seems to maintain the proper temperature better.