наготове, к услугам
наречие 1) общая лексика наготове, к услугам 2) общая лексика по требованию
or on call phrasal 1. a. available for use; at the service of Example: thousands of men at his call b. ready to respond to a summons or command Example: a doctor on call 2. subject to demand for payment or return without previous notice Example: money lent at call