I know with Fido that you can choose how the money you put on is going to be used ($1/day unlimited incomins as an example. Or you can opt for using the money as, at $0.30/min. Fido will work in the US, just be charged for roaming.
Solo, as far as I know is about $0.30 - $0.40/min, with no other choices to change for unlimited incoming or evenings or weekends. I don't know if it would work in the US, but generally, prepaid phone sdon't work down there because of high roaming rates.
