To summon someone to a place for a specific purpose. The manager decided to call in the team for an emergency meeting.
To request the return of something, especially a loan or debt. The bank decided to call in the loan after the borrower missed several payments.
To report one's presence by telephone. She had to call in to work to let them know she would be late.
To request help or advice from someone, especially an expert. The company had to call in a consultant to help with the project.