I got what you tried to say. I just wanted to underline that American and European LTE in general is compatible and that one day there will surley be devices that support the different frequencies so transatlantic roaming will be possible.
Btw Apple is facing trouble in many countries for advertising the new iPad as "4G" despite it only works only on American LTE networks:
Denmark, Sweden, UK, New Zealand also probing Apple’s “4G” marketing for the new iPad