The cell phone companies all claim to offer data access at "4G" speed, but each company has its own idea about what that means. Wall Street Journal tech writer Walt Mossberg helps explain what each company offers.
http://allthingsd.com/20120327/4g-or-not-4g-a-guide-to-cut-through-all-the-fast-talk/
One point to remember: LTE (Long Term Evolution) is a family of technologies, and one carrier's LTE phone almost never works on a different carrier's network. At this point, you're much more likely to find HSPA+ service that works with your phone when traveling outside USA.
http://allthingsd.com/20120327/4g-or-not-4g-a-guide-to-cut-through-all-the-fast-talk/
One point to remember: LTE (Long Term Evolution) is a family of technologies, and one carrier's LTE phone almost never works on a different carrier's network. At this point, you're much more likely to find HSPA+ service that works with your phone when traveling outside USA.