Interesting. Somewhere I've picked up the idea that it's the height of rude to call people by their first name in American unless they say it's okay. I'm thinking that it's probably best to err on the side of caution. Thanks for the different perspectives.
Totally depends on the circumstances. Most adults use first names with each other, but there are some exceptions:
- adults whom you have known since you were a child (I still call my parents' friends "Mr. and Mrs. Lastname")
- ranking military members
- people who are much older than you are (sometimes)
- people in major positions of authority (a judge while in court, a doctor while at the office, etc.)
- the media - newspaper articles will almost always say "Firstname Lastname" the first mention and then "Mr./Ms. Lastname" for the rest of the article, and same goes for TV or radio interviews
- strangers or almost-strangers in professional positions of power.
This last one is tough because it's not black and white - some salespeople will call you "Mr. Lastname" and others will try to skip straight to "Firstname" as soon as possible. Most medical professionals will refer to you by your last name when you're a patient, but if you see your doctor in a social situation outside the office you could call each other by first names, you might call him Dr. Lastname, or you might just call him "Doctor." Some clergy go by "Reverend Lastname" while others prefer "Pastor Firstname" instead (and this varies by congregation). The CEO of a small tech business is likely to go by his/her firstname to the employees, but the CEO of a larger company is probably "Mr./Ms. Lastname" from most of the underlings and in the third person.
There's really no way to tell until you get there and see what everyone else is doing. If all else fails, ask your partner's relative what your business contacts prefer to be called.