Interesting. So what I'm thinking is your asking if IM would have events listening to the text to see if "phone" or "mobile number" come up and when they do, the next reply will be encapsulated with the <phonenumber> tag.

I would say that is a tough call. I would think that SmartTag type of technology could help you there, yet I don't think it would be 100% successful.

Then again, I don't work at MSFT.