Limiting the conversation

Perhaps a limit could be built into the system so that a call doesn't get out of hand and someone talks for "hours". It would be helpful if a friendly message could be played automatically after a freely definable time, say ten minutes. For example:

"Thank you very much for the pleasant conversation. If you have no further requests, I'll say goodbye at this point and wish you a nice day."

This would prevent someone from blocking the answering machine for a longer period of time without appearing rude.