You didn't mention which exception you got, but it sounds like you're probably getting `NotSupportedException: the member "[whatever]" has no supported translation to SQL error".
If you search for this exception you'll find a lot of answers along a common theme - essentially Linq2SQL doesn't know how to translate "Type" into SQL so it falls over. In your case you can fix this by using Linq2SQL and Linq2Object:
// L2S from the DB, transferred to an Enumerable
var itemSource = (from c in dc.Contacts select c).AsEnumerable();
ContactListBox.ItemsSource = itemSource.Where(c => c.Type == "q");
// or full form Linq
ContactListBox.ItemsSource = from c in itemSource where c.Type == "q" select c;
In my case I didn't add a column, I just added multiple contacts with different Type
s and filtered only the ones of Type
"q".