It’s not necessarily a “new rule” but it is a significant change in the way people communicate.
My job is to “help companies think differently” so consider the way you leave messages for people.
This NYT piece presents arguments for the impending death of voice mail. And I have to agree. I’d much rather receive a TXT, email or visual voice mail. VERY interested in a new Google project that will marry voice messages with email or TXT.

Interesting blog post. What would you say was the most important marketing factor?
John, If I understand your question correctly:
The key marketing takeaway from this is the need to speak to your audience in a language they understand. If you are running a campaign in France, it makes sense to deliver the message in French, etc.
I have started asking those with whom I have significant interaction for their preferred means of communication and I have become pro-active in telling people what I prefer.
On a grander scale, as communication channels shift so will the advertising messages that grow along side. Billboards did not come into fashion until Americans started driving faster on inter-city highways. Keep an eye on advertising opportunities in mobile space and elsewhere.
Is that where you were headed?