Dial the 800 number on your bill or 611 from your wireless phone to be sure. Within credit limits, you can have as many phones on your account as you want. To consolidate the billing, all phones must be with the same carrier. Your provider outlines the boundaries of your calling area. You can refer to the providers' website or with the literature you received with your phone for specifics.
Some carriers disable the international function as a security measure.
If you are authorized to do so, contact your provider and make sure you have access to international calls. There are not many more than four things that could make your phone not work. If there is a problem with the carrier's network, they should be able to tell you. If the phone is defective, you will probably need to get it replaced by the store you purchased it from. This is called crosstalk.