There are two groups of people in the world - those who know when to walk away from their computer and those who are tied to it 24/7. The former group will therefore hate this hack - and will wail about it in the comments. The latter group will love it. Unfortunately, I am in the latter group!
There is a plug-in available for Pidgin called gSMS which will notify you by mobile phone SMS when someone tries to contact you by Pidgin and you don’t respond within a specified time frame. This would be useful if you had to step away from your desk but you were expecting an important message. By configuring this plug-in, you can be told by SMS that the person left a message and you can get back in touch with them as soon as possible.