Originally Posted by alanw
I'm not sure if the OP is asking if he can use them at the same time. If that isn't the case, then yes, you can have a plan with each vendor and switch between the two depending if you want to use data (or be in the US) or voice in Canada.
Otherwise, Scooby is right.
You could be right, if the OP does indeed want to use 2 sims at different times, then the Treo will have to be unlocked (do a google search on that).