It is possible if someone writes a small application for it. The database that stores all the text messages contains the number where the text came from (remote_uid column in Events table).

Writing a small script that reacts on every received SMS, and then updates the contact information, adding a new property (or modifying it if it already exists) "Last text from" and add the phone number in that.

What would happen for the user workflow is that after reading the text, the user could click on the avatar, and click on that property.

I'll put it on my to-do list. Can't promise any delivery dates though.