Delete duplicate Item in ObservableCollection ? In Windows Phone 7

How can I do to delete duplicate item in ObservableCollection

Class Customer has got string Name, string PhoneNumber

If I'm add Name = Jonh in first time - OK

In second time i'm add Name = Jonh (duplicate) <-------------------- How can I do to delete duplicate item ?

(When we're Delete duplicate Name, What happen to PhoneNumber? )

Name :                                   PhoneNumber:

  Jonh        123

  Jane113

  Jonh<----Delete                                      456