I live within a few minutes of the US/Canadian border and cross frequently. My problem with ATT was that my phone would try to hold a weak ATT signal in the border region and I finally got ATT to push to my iPhone an update which would allow me to manually force my phone to a US or Canadian carrier even when a US signal was detected. I spent hours on the phone arguing with people to get it and customer supported originally denied it existed. I had to remain firm, polite, and a little bull headed to get the update through.