Yes, I've mentioned Televox here before. It was essentially a way to provide a service of lots of information but using only the bandwidth of one teletext page. It worked using the little-used 'time page' function, I think the only other the use was for the Ceefax Alarm Clock.
They had a regular Oracle page which gave instructions and the phone number, and the page the service was on was 700 (or 777?). On p700 you would see other peoples pages flash up very briefly, the way it worked is that these had a time page number that was given out when you called, so when you typed that into the time field it grabbed that page and kept it on your screen. You then navigated it on the phone with voice commands, or I think DTMF tones.
There were two ways you could see it without phoning and therefore paying and they were by guessing the 4 digit number (unlikely) or by pressing Hold just at the right moment....but of course if you did that then you'd only see what was on there at that moment and it wouldn't change as the legit user navigated
No idea who provided it but I do remember seeing that it was a company called something like Macallum, odd how details like that stick in your mind..... and a quick google provides this:
Here's a screengrab: http://www.teletext.org.uk/index.php?cat=30_Archived-nbsp~Pages&page=20_Oracle-nbsp~1992&zoom=171