For both the lazy and the really sick, Call-in-Sick lets you pre-record a message to give to your boss when you want to skip out for the day. All you have to do is call the number, record the message multiple times to get the right amount of phlegm in your voice, and schedule the delivery time.
They also note that you should test this out before your actual sick message with a "Hey boss, call me back", so it doesn't fail on you when it matters. The message goes directly to your boss's voicemail, so no one's the wiser. Adam of Lifehacker also notes that you can use this to send you or your family reminders in the future, such as "remember to buy some milk you ungrateful shrew"—for the wife.