If you buy EU SMS games you can play them on the NTSC console.
[1] IS EUROPEAN SOFTWARE COMPATIBLE WITH U.S. SMS UNITS?
Yes. Although folks may be wondering about PAL and NTSC definitions, there
appears to be only some minor problems playing European games, and only
with a small minority of carts:
From -http://www.classicgaming.com/museum/faqs/smsfaq.shtml
If you want to play a EU system in the US i think all you need would be a power and video converter due to the difference in plugs.