no adapter cable will work with your focus , im 99% sure that the OS doesn't support it at all. but I cant find proof , lol and if it does it would only be on new WP ( titan 2 , Nokia 800/900 )
regarding the Connection.
HSPA(+) ( real 3G ) supports up to 21MB sec
LTE (real 4G) supports up to 75mb sec
the Samsung FOCUS radio only supports up to 7.2MB sec
long story short , dont worry about faster speeds cause your caped at 7.3mb.
the Iphone 4S caps out at 14.4 Mb sec
what does this all mean? you dont need 4G.....
dont be fooled by marketing scams.