My boss doesn't like to take calls that he's not expecting but I'm not always sure who he's expecting.  If a client calls and asks to speak to him, I ask who is calling and find it easiest to say "let me see if he's available".  When he says he can't/won't take the call I ask to take a message and let them know he will call back.  He doesn't like when I politely say "let me check" because he thinks it's obvious to the caller that he's here but just doesn't want me to take the call.  What is the best way to politely check if he's available without letting the caller know my boss is screening?  I sometimes will say he's on a call or in a meeting but I can see if he'll be done soon but I feel like that sends the same message.  Suggestions?