I was a Demon customer for many years, not in the first batch but signed up in the first year. My local exchange back then didn't even support DTMF so dialling in was slow. My old 158.152 address still resolves but to a different hostname now.
As for email, I saw the light on that one back in 2000 when I registered the domain I still use today, which is based on my Demon hostname. I eventually jumped to AAISP because Demon weren't rolling out IPv6 and I wanted to go play with it.
I still ping gate.demon.co.uk as a connectivity test even now, I guess I'll have to stop that.