MobileIron allows you to designate "active" and "inactive" countries. Once you have designated a Country as inactive all attempts to setup devices in that country will be blocked with the user receiving a "Unable to Connect to the Server" error message like the one below in iOS;
To make changes to the country lists log into the MobileIron admin portal;
Click on the "Settings" page at the top and then scroll down to the registration preferences section;
In this section you have the list of Disabled and Enabled Countries. To change the configuration just select the country in which box and click the appropriate arrow to move it between the boxes.
Once you've made the changes click on the "Save" button at the very bottom of the page.