Effectively impossible since the email address consists of both a user name and a domain name, which is owned by the ISP. Waaay down in the bottom of the plumbing of the internet in a thing called the DNS protocol and also SMTP protocol, there's only one place that a domain name can go when sending mail. I could get all geeky and describe how it all works, but it would go over pretty much everyones heads, so I'll stay away from that area (In past lives I have written both a DNS stack and an email stack). However, for the simple explanation, the domain name is like a physical street address. Just like you can't take your street address with you, you can't take your email with you.
If you want a portable email address, don't get one from your ISP. Use one of the many generic providers such as Google, Yahoo, Microsoft (nee live, nee Hotmail) etc etc. If you really insist on using ISP for your emails (generally a bad idea), then still sign up to google et al and use their forwarding capability.