Hmm. I work in academia. It is customary when writing to a prof for the first time "Dear John (if I may)". Occasionally about once every three years somebody objects. Oh and upon promotion it's usually rather lovely to call a colleague Professor Bliggs a few times.
Generally I am happy with first names terms providing it is a mutual thing. My old bank used to call me Mrs Roses, my new bank is first name and I'm just grateful they are open every day, often until 7pm.
I don't like the overfamiliarity of the sales call. "Hey there OhThe are you having a ?×good day" but I don't have to engage with it and usually respond with "I'm awfully sorry but I don't think I know you, would you mind telling me where you got my number".
I use the first name of most professional people I come across and they use mine. That goes also for my hairdresser, painter, gardener, etc.
What I will not countenance is another professional, always a Dr using my first name and introducing themselves by title. No I will not have that and always correct it. Similarly if the nurse refers to that Dr by their title, the nurse may not refer to me by first name as it implies I am subordinate to the Dr. It is an equality issue and one used to subordinate the patient. Even worse is when one sits in the waiting room and all the men ade called as Mr Brown and Mr Smith but the women are called as Jane Smith or Mary Jones. I see no reason for men to be afforded more courtesy than women and would have no issue if the men were called without a title. One has to wonded why this should be so when the nhs is supposedly so hot on equality and diversity. Neither do I answer to Love or Darlin both commonly used by nursing staff in hospitals near me. My children of course call me mum - hcps may not. It is reductive.
I am happy to have my first name used by any individual who allows me and their less senior colleagues to use theirs. Any human who expects me to address them with a title may use mine. "Hello OhThe, I am Mr Gascoign" "I am very pleased to meet you Mr Gascoign, I am Mrs Roses" "Oh, err, you can call me Paul" all well and good but the relationship was already blown by the assumption that I was a subordinate stakeholder in relation to me care. It is a very out of date attitude and extremely patriarchal.