1. To communicate (with) by telephone
2. To summon to a particular activity or employment; SYN. call for.
3. To summon to enter
4. To take a player out of a game in order to exchange for another player.
5. To take out of circulation when it is useless or defective
6. When you call your place of employment to say you cannot work that day because you are sick, you call in or call in sick.

Allowing listeners to engage in broadcast telephone conversations with the host or a guest

When you request the help of people or of an organization with more experience, power, or knowledge to help with a problem or difficult project, you call them in.