Just a quick note that if you are on Koodo Prepaid and purchase US roaming boosters, your phone will NOT work in the US if you simply set your phone to roam and automatically choose networks. While this will suffice for other carriers, it doesn't work with Koodo. I found this out the hard way, when I paid for the boosters (talk, text, and data) and set my wife's phone to roam and to automatically choose networks. Problem was, when she hit Seattle, she realized she had no service! She was choked, as she badly needed GPS and was relying on her phone to keep in touch during a family health crisis back at home.
Long story short, I ended up driving to Seattle (!) to help her out, only to find that you need to manually choose the AT&T network on the phone while in the USA in order for the prepaid roaming to work there. Koodo needs to publish this in their "how to" section about getting prepaid roaming to work in the US. This lack of information caused us stress, time, and $.