I did a bit of research into the way the Google Call Conversion script dynamically changes phone numbers, and, as I suspected, the numbers do change based on location, offering either an equivalent to a local number, or a local number (if not toll free). This then allows you to track the caller’s location and obtain conversion data from that. Google offers an excellent explanation of how this works, as well the countries for which they offer dynamic phone numbers.
To create dynamic phone numbers using URL parameters, you could use Unbounce’s dynamic text replacement feature and dynamic keyword insertion in AdWords. (The hyperlinks above contain explanations of how these functions work, and step-by-step instructions on getting them set up.)
There’s probably a way to do it using some custom scripts, but this should get you started in the meantime!
Let me know if this is helpful