Is it possible to use a Sprint Sanyo dual-band phone in other countries?
Yes, it is possible. I know that sprint has this capability with certain dual band phones. Call this number: 1-888-226-7212.
This is the Sprint's international roaming team. They'll tell you if your phone is one of their international phones and can get you set up on an international plan.
Bear in mind that not all countries will have the frequencies that your phone will operate on so you might be out of luck in some places. The best is to get a quad or tri band phone.