i. "I don't know". Instead, say: "That is a good question; let me find out for you" or offer to connect the caller with someone who could provide the answer.
ii. "I/we can't do that." Instead say: "This is what I/we can do."
iii. "Just a second" Instead: Give a more honest estimate of how long it will take you and/or let them know what you are doing.
iv. "No." Instead: Find a way to state the situation positively.