I have kind of wondered about that too. For awhile, my wife was deleting them once she learned now. She may do that again, but yesterday she left them all on there, and hasn't tried overly hard to keep the phone hidden from me.
She's also text-messaged him in the presence of our daughters last weekend, while they were out shopping together, but that seems to have stopped now that I set some boundaries (didn't confront her on OM [altho I've done all but!], but did tell her I would no longer tolerate COMMENTS in front of our Ds that were disrespectful towards me.)