Comment by ErroneousBosh

There actually were ones that did interactive chat, but that required a modem too.

For teletext it would display 40x25 text with eight colours (the colour control codes took up a character space) and simple block graphics, which was stored in the first 25 lines or so above the top of the screen.

In the UK, the BBC ran Ceefax and ITV ran Teletext, which you could access with a button on your TV remote. These days it's actually possible to recover them from VHS recordings with really careful analysis (the bandwidth wasn't really there for it to work with a naive data slicer). During the day BBC2 ran "Pages from Ceefax" with some library music behind, when it didn't have Test Card F up (making Carole Hersee the most broadcast face on British TV, probably even to this day).