1) to pay a visit, especially a brief or informal one:
Call in if you are in the neighborhood.
2) to demand payment of:
The bank can call in the loan at any time.
3) to take (something) out of circulation, because it is defective or no longer useful
The makers have called in some cars with dangerous faults.
4) to summon to one's assistance they had to call in a specialist:
The government then called in troops to deal with the disturbances.