I remember doing something similar to get ISP access in the early 90s. Like AOL various ISPs would be bundled into CDs/floppies and offer a free trial.
One of them did not validate the card number, so you could just type in 000000000000 or whatever and your free trial was enabled for a month or whatever and then be auto cancelled when they tried to bill for your first month after the trial. In the UK though local calls were not free and charged by the minute.
I think that ISP also bundled a <1.0 version of Netscape's Mozilla (0.8?) on their disk which was nice as otherwise I only had mosaic.
When the first Palm VII's came out (https://en.wikipedia.org/wiki/Palm_VII) I wanted to see how responsive the wireless connectivity was before buying one. The local Staples store had a functional demo unit, but it had no subscription. So I tried signing up with random info, when it got to entering a card number, I entered 4111 1111 1111 1111, which passes the basic validation checks for a visa (and is obviously easy to remember). The device activated immediately and I was able to try some live data transfers. It worked for about 3 days (I went back to check it out of curiosity).
Presumably the activation of service happened locally in the device, or with minimal cross-checking with the backend billing service.
A few months later I tried it on another unit and the number no longer worked for activation :)
One of them did not validate the card number, so you could just type in 000000000000 or whatever and your free trial was enabled for a month or whatever and then be auto cancelled when they tried to bill for your first month after the trial. In the UK though local calls were not free and charged by the minute.
I think that ISP also bundled a <1.0 version of Netscape's Mozilla (0.8?) on their disk which was nice as otherwise I only had mosaic.
Good times.
Edit: I think the version of netscape/Mozilla was this one - I distinctly remember the "M" logo that would rotate as pages loaded slowly on a 14.4 modem: https://www.webdesignmuseum.org/uploaded/old-software/web-br....
Curious that it was called "mosaic netscape" - I don't remember that.