I will leave my original answer in place but the below is how you need to approach it.
(Forgive me but it is a long time since I have used regular asp.net / web services with jquery:)
You need to use the following js lib json2 library, you can then use the stringify method to ensure your json is in the correct format for the service.
var dataO = {
numberId: "1",
companyId : "531"
};
var json = JSON2.stringify(dataO);
$.ajax({
type: "POST",
url: "TelephoneNumbers.aspx/DeleteNumber",
data: json,
contentType: "application/json; charset=utf-8",
dataType: "json",
success: function(msg) {
alert('In Ajax');
}
});
UPDATE: Same issue / answer here
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