In Portuguese from Portugal, we like to say answer the phone with "to", kinda like pronouncing the word tow but without the w. It's a shortened version of the word "estou", which translates more or less to "I'm here".
Well, I've never heard of anyone saying "diga". Where I live, we just say "hola" or just "hey" (I say hey when that person is a friend or someone I know).
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