call in
• enlist someone's aid or services.
• "you can either do the work yourself or call in a local builder to help you"
• require payment of a loan or promise of money.
• "the bank would call in loans and foreign donations"
call-in
noun
• a radio or television programme during which the listeners or viewers telephone the studio and participate; a phone-in.
on call
• (of a person) able to be contacted in order to provide a professional service if necessary, but not formally on duty.
• "your local GP may be on call round the clock"
• (of money lent) repayable on demand.
