In this case I think you should be the one to say hello..
I you wanted to add me to msn and I accepted your invitation, you were the person who initiated adding eachother to msn.. Therefor I would expect you to be the person who has something (perhaps really important) to share with me.. 
And ofcourse the same if things were changed around.. If I wanted to talk to you and added you to my msn, you accepted.. Then I would contact you first..
but this is just worth about 2ct..