Can I take a message?
An offer to transcribe someone's message to someone else who is currently unavailable. A: "Can I speak to Josh?" B: "He's not available right now—can I take a message?"
Could I take a message?
and Can I take a message?; May I take a message?the phrase used on the telephone to offer to take a message and give it to the person the caller is seeking. Bill: Can I talk to Fred? Mary: He's not here. Could I take a message for him?