How can I switch from my ISP's mail to gmail? I understand that I should, but I can't notify all my contacts!
As I've said many times, the problem with using an email account provided by your ISP is that if you change ISP's, that old email account stops working. That can be more than annoying, so the time to fix that is now.
First, go get a gmail account (or AOL or Yahoo or Microsoft - anything not tied to an ISP). That's easy enough, but how to get everyone to start using it? The simple answer is to let that happen over time.
Start by forwarding your current email to your new gmail address. That's usually easy to do and if not a phone call to your ISP should take care of it. All your email will now show up in your gmail account and you can read and reply to it there.
When you see important email from your bank or wherever that is still using your old ISP address, go fix that. That kind of thing will dribble in over weeks or months and it doesn't matter if you miss it this time; you'll fix them up with your gmail address the next time. Eventually you'll have all those things updated.
For your friends, just add a note when you reply: "By the way, my new email adress is..". Of course some will ignore that the first time and the second and even longer, but eventually they'll catch on and start using the gmail address.
That's it. You don't need to explicitly cancel your old email. However, after a while you'll notice that the only email still using it is junk that you do not want, so at that point you might want to take off the forewarding or tell the ISP to just can it. That's up to you - you can leave it as is forever.