Yes you can use prepaid SIM while traveling with the Storm. All you have to do is give Verizon a call and they will unlock the Storm for you with no charge. The SIM card is removable, it is a little hard to remove it the first time but it will come out. My dad just traveled to Albania and took his Storm with him and has been using a prepaid SIM to call us.
NJBlackBerry is correct BlackBerry data is not available.