Truckondo
macrumors 6502
If you travel internationally (from the US), my advice would be to stay with AT&T. Most other US based carriers are horrible outside the US --- Verizon being the worst...more a function of who their local carriers are I would suspect. I spend well over half my time traveling outside the US (Europe, Asia, Japan, Africa, South America). I had AT&T for several years and was forced by my company to switch to Verizon 2 years ago. Where with AT&T the service was "transparent" wherever I went globally, with Verizon I experience a succession of dropped calls, limited to no data service, etc. Also, Verizon's inability to handle cellular and data at the same time is a pain.
I would think T-Mobile to go international. They give you unlimited text & data (128Kbps but free ) in 100 countries. AT&T will charge roaming fees. I got hit with a $30 charge because I had to check an email when I travelled to Spain a couple of years ago. In the end though it comes down to the coverage in your area. I'm actually switching to T-Mobile today and I'm waiting for the UPS guy to bring me the phones. We'll be finally LTE equipped.