I go to the US for 3 weeks holidays in a few days.
My One X is the international one, can I get the 50$ monthly unlimited plan with unlimited data or do I need the 25$ Monthly Plan + 25$ 1GB Data Plan?
Someone wrote he uses a cell phone unlimited data plan with his international phone without problems.
Also, which APN is best of all APNs that are floating around here? I'd like to have HSPA+ speeds
Read this in the SGS3 forum, the same applies for the One X. As for the APN, it should pick it up from the SIM without you having to tweak it. I'm using a UK phone on AT&T and it did. AT&T's HSPA+ network isn't everywhere yet but it's in most major cities. You should get from 3-8MB down. In non HSPA+ cities you should get between 2-3GB down.
http://xdaforums.com/showpost.php?p=29410822&postcount=1160