After confirming a dinner reservation, the hostess requested my e-mail address "for our mailing list."
While complying would certainly qualify as an opt-in, telephone dictation is just too dangerous a tactic for building a list. Typos, misspellings and mis-hearing (was that 'b' as in "boy or 'v' as in "victory"?) will inevitably result in unhygenic lists. That, in turn, will negatively impact deliverability of the entire list.
They know I'm coming in for dinner anyway. Why not ask then, if they have to ask? Some restaurants are beginning to leave a card with the bill requesting an opt-in to e-newsletters. That has its risks, too (handwriting isn't always crystal clear). But it has to be better than a game of telephone.