- fixed network operators;
By Fax and Email. Circular letter to. - fixed network operators;. - mobile
network operators;. - external fixed network operators;. - inter-operator
SMS operators ...
<http://www.google.com/url?sa=X&q=http://www.ofca.gov.hk/filemanager/ofca/common/Industry/telecom/circular_20120413.pdf&ct=ga&cad=CAcQAhgAIAEoATAAOABA043B_ARIAVgAYgVibi1VUw&cd=WJPcbVr9FRg&usg=AFQjCNHnHqaoydN39o2ANYS2JxDGy7OcgQ>