What does it mean when someone says they will call in a bit?

Could you please clarify the meaning behind the phrase "they will call in a bit"? Is it a casual way of saying they will call soon, or does it imply a more specific time frame? Does it depend on the context in which it's used? Additionally, is it commonly used in formal or informal settings, and does it vary by region or culture? Understanding this phrase's nuances could be helpful in avoiding misunderstandings in communication.