As I understand most that still use their Minitels use them as a digital phonebook next to their old phones. I mean, If you have inputed tons of numbers in to any device and it works reasonably you won't change easily.
For those not familiar with Teletext, here is an online portal as an example: http://www.rtbf.be/services/teletexte/ - some teletext services even offer chatting via SMS messages, which then show up on the TV screen.