Married couples calling each other Mr. and Mrs. is rather more 18th century, Joao.
In Jane Austen's 18C Pride & Prejudice, the moderately well-off parents of the heroine call each other Mr. and Mrs. Bennett in front of other people. What they called each other in more private moments is not revealed, but possibly "My dear" would satisfy both custom and affection. Their daughters, however, seemed to call their partners / spouses by their christian names, which suggests times were already changing. They still tended to refer to them with others as Mr. though. Sometimes it seems that, amongst close peers - sisters, friends etc. - they referred to them by only their surname e.g. "My dear Bingley ...". So this convention, in England, was changing over 100 years before the Titanic disaster. What is true, however, is that in 1912 some of them still might have referred to their husbands / wives as Mr. / Mrs. in conversations with comparative strangers, or people of a lower social order.
But how times change. I answered the phone the other day to hear a cold-calling salesman, in a call centre in Bangladesh, cheerily ask,
"Is that you, Monica? Mohan here!"
Now, even though I'm perfectly used to everyone here in face-to-face situations immediately calling me "Mon" - from the postman to the local MP - I did find this rather annoying.
