A countable unidimensional theory without the omitting types order property (OTOP) has prime models over pairs and is hence classifiable. We show that this is not true for uncountable unidimensional theories.
"An Unclassifiable Unidimensional Theory without OTOP." Notre Dame J. Formal Logic 38 (1) 93 - 103, Winter 1997. https://doi.org/10.1305/ndjfl/1039700699