Roboblob: http://blog.roboblob.com/2010/01/19/modal-dialogs-with-mvvm-and-silverlight-4/

JoshSmith: http://www.codeproject.com/Articles/70223/Using-a-Service-Locator-to-Work-with-MessageBoxes
-> article comment:  http://www.codeproject.com/Articles/70223/Using-a-Service-Locator-to-Work-with-MessageBoxes?msg=3427352#xx3427352xx

StackOverflow answer: http://stackoverflow.com/questions/5916930/using-mvvm-in-wpf-should-i-lauch-child-windows-from-view-code-behind-or-viewmo