@OP: if you're unsure about an area code, you can look it up. If you see it in your calling history, I know Android phones are pretty good for displaying the Country/Province or State and even city of origin of the phone number.
To save on long distance calls to the US, if you have wifi or data coverage, you can make the outbound call via Hangouts Dialer. Free calling to Canada/US via Google Hangouts (on Android make sure to download and install "Hangouts Dialer" from Play Store). You can even configure it to display your cellphone number on outbound calls.