Yes. As an example, suppose you want to allow calls and SMS messages only to numbers in the North American Numbering Plan (NANP).
The country code for the 20 countries in the NANP (which includes the US, Canada, and countries in the Caribbean) is +1. You can find lists of area codes online. The Plivo prefix consists of the numbers of the country code plus the area code: 1406 for Montana, for example.
Allow the prefixes you want to include in your application, and have your code check to make sure that any attempts to message or call any other prefix will not be completed.
You can achieve the same results for outbound calls or messages for entire countries by going to the Plivo console, to Voice or SMS > Geo Permissions > Country Permissions, and ticking checkboxes to enable or disable calls for specific countries.