US roaming add-on are for when you travel to the united states. With them you can make and receive calls from the US, text from the US and use data from the us (if you get one with data). These are not your usual limits tho! Each add-on has it's own allowance and it is not what is part of your monthly plan. With you calling minutes, you can place calls to any US number and any Canadian Number, from the US. This does not include calls to the US while in Canada.