"The mobile phone you are trying to call is presently busy."
A common enough mistake, actually. But a wonderful opportunity for a little Ad Nausea and a chance to be patronisingly educational. 'Presently' means 'soon' .. as in 'Vodafone will presently re-record this message'. The correct word to use would be 'currently', or the phrase 'at present' .. as in: The mobile phone is currently busy, or The mobile phone is busy, at present.
Ah, the Internet! Font of information! Aren't you glad you read this blog? Meanwhile, I am currently running low on cigarettes, so I shall presently hop out to buy some more..