Other than enabling your account to allow international calls you will have to submit an ID (through you voip.ms account) to be cleared if you want to call to any one on the list "questionable" countries. High incidences of fraud linked to those countries probably have something to do with it.
These countries are
Afghanistan, Albania, Algeria, Andorra, Angola, Anguilla, Armenia, Australia, Australia Territories, Azerbaijan, Bangladesh, Belarus, Benin, Bhutan, Bosnia & Herzegovina, Botswana, Brunei, Bulgaria, Burkina Faso, Burundi, Cameroon, Cape Verde, Central African Republic, Chad, Comoros, Comoros, Congo, Cook Islands, Croatia, Cuba, Dem. Rep. of Congo, Egypt, Equatorial Guinea, Eritrea, Estonia, Falkland Islands, Faroe Islands, Fiji, French Guiana, French Polynesia, Gabon, Gambia, Georgia, Ghana, Gibraltar, Guinea, Guinea Bissau, Guyana, Honduras, Hungary, Iran, Iraq, Jordan, Kenya, Kyrgyzstan, Laos, Latvia, Lebanon, Lesotho, Liberia, Libya, Lithuania, Macau, Macedonia, Madagascar, Malawi, Malaysia, Maldives, Mali, Malta, Marshall Islands, Mauritania, Mauritius Island, Micronesia, Moldova, Mongolia, Montserrat, Morocco, Mozambique, Namibia, Nauru, New Caledonia, Niger, Nigeria, Niue Island, North Korea, Oman, Papua New Guinea, Reunion Island, Romania, Russia, Rwanda, Sao Tome & Principe, Senegal, Serbia, Sierra Leone, Slovakia, Slovenia, Solomon Islands, South Africa, Sri Lanka, St. Helena, Sudan, Suriname, Swaziland, Syria, Tajikistan, Tanzania, Togo, Tokelau, Tonga, Tunisia, Turkey, Turkmenistan, Tuvalu, Uganda, Ukraine, Uzbekistan, Vanuatu, Wallis & Futuna, Yemen (Arab Republic), Zambia and Zimbabwe.