1. I am calling instead of Mr. Frank.

2. I am calling in place of Mr. Frank.
3. I'm calling on behalf of Mr. Frank.
4. I'm calling in lieu of Mr. Frank.
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Are they all the same in meaning?
Which ones are commonly used? Do you have some other similar expressions?

Yes, they all mean the same thing. We would use #3 most often, though.

Well, although all four ways of saying it might be intended to mean the same thing, they could be interpreted differently. If you are speaking instead of Mr. Frank, perhaps you are speaking for yourself, not Mr. Frank. If you are speaking "on behalf" of Mr. Frank, that is clear that you are representing Mr. Frank and what he might say.

1. "I am calling instead of Mr. Frank."

2. "I am calling in place of Mr. Frank."
3. "I'm calling on behalf of Mr. Frank."
4. "I'm calling in lieu of Mr. Frank."

These expressions have similar meanings, but there are slight differences in usage and connotation.

1. "I am calling instead of Mr. Frank": This expression suggests that you are making the call as a substitute for Mr. Frank. It implies that Mr. Frank was originally supposed to make the call, but you are doing it on his behalf.

2. "I am calling in place of Mr. Frank": This expression conveys a similar meaning to the first one. It indicates that you are making the call as a replacement for Mr. Frank, who may be unavailable or unable to make the call himself.

3. "I'm calling on behalf of Mr. Frank": This expression also implies that you are making the call on Mr. Frank's behalf. It suggests that you have been given the authority or permission to act as his representative in this matter.

4. "I'm calling in lieu of Mr. Frank": This expression is less commonly used and more formal. It means that you are making the call as a substitute for Mr. Frank, often in a professional or official capacity.

In terms of usage, "I am calling on behalf of Mr. Frank" is the most commonly used expression. It is often used in business or formal contexts when someone is calling to represent someone else's interests or deliver a message in their place.

Similar expressions include:
- "I am speaking for Mr. Frank"
- "I am phoning for Mr. Frank"
- "I am making this call on Mr. Frank's behalf"

Overall, while these expressions have slightly different nuances, they all convey the idea of making a call on behalf of or as a substitute for Mr. Frank.