“Glad you called, but I just am not able to entertain you right now. However, if you are offering to buy dinner, I may be available sooner than you think. Don’t forget to leave your name and number, so I don’t get mixed up with different offers, and go to the wrong restaurant. Bye!”
You could use this website as a free voice over generator for narrating your videos in cases where don't want to use your real voice. You can also adjust the pitch of the voice to make it sound younger/older, and you can even adjust the rate/speed of the generated speech, so you can create a fast-talking high-pitched chipmunk voice if you want to.

"Hello? ...Hello? ...Hellooo? I'm sorry, you're gonna have to speak up, I can't hear you... That's 'cuz I'm not home! Leave a message.
My 12 y/o niece put on her cell phone message, "Leave your name and number. If I love you, I'll call you back." Although not earth-shatteringly funny, it was cute the way she said it. In college my roomate was a cop, he told me that the worst things you can say on an answering machine were 1) telling them your name, 2) telling the caller your number, 3) and that you aren't at home. Well, here's what I did... Thats probably good advice for a home phone, but at the same time, I don't think it applies to a cell phone really. I used to have a longer message aimed at keeping people from leaving messages ... but I hate getting voicemails for the most part. One summer I had my little cousin start singing take me out to the ball game, I cut him off after a few lines, but it was just my version of satire against parents who have their kids sing, and it was pretty funny.