Sorry, this is a bit off topic of your problem at hand but wanted to follow up a bit on djk7 & Loren Pechtel's suggestions.

I completely agree that it's wise to set up a consistent e-mail address. Hotmail/Gmail/Yahoo is certainly a way to address that matter.

I prefer having a permanent e-mail address that doesn't look like a free account so I registered my own domain like djk7 stated. The .info TLDs are very inexpensive to get, but if you can find a .com or .net name that you like you can register it for about $10/year. Once you own the domain there are several ways to set up e-mail accounts for free.

Assuming:
1. You registered rove312.com
2. You have a freebie account [email protected] from your new ISP.
3. Your son moving to college has [email protected] and wants a cool new rove312.com address.
you can...

a. Use e-mail forwarding from your registrar.
Log on to your registrars website and enable forwarding...
[email protected] forwards to [email protected]
[email protected] forwards to [email protected]
(repeat for as many accounts you like)

Now in your comcast account change the Reply-To address to [email protected]
Likewise have your son change his hotmail Reply-to address to [email protected]

Voila, to the rest of the world you look like [email protected] even though you are using your ISP's e-mail facility for inbound/outbound traffic. If you change ISPs again just reset the forwarding to your new freebie account - transparent to the rest of the world.

b. Use google apps to host your mail.
Google will provide up to 10 mailboxes for free
http://www.google.com/apps/intl/en/group/index.html
It does take some work but once set up is pretty bulletproof.

c. Set up your own mailserver (I did but this requires some nerd skills, having a pocket protector and slide rule helps)

Anyway the base solution using forwarding is really simple and can get you and yours an inexpensive unique e-mail addresses for life. Good luck on getting a grace period on sbcglobal.net