It sounds like you are paying for wireless internet service through Alltell, so you shouldn’t need to be paying Earthlink any more. I’d give them a call first to make sure- 1-800-alltel1. Yes, anyone can sign up for a free email account with G-mail.
Yes, you should be able to drop Earthlink now that you have the Alltel thing working.
One thing you will want to do if you are using Earthlink’s e-mail, is not only set up another e-mail (like gmail or yahoo for free), but you may want to grab any mail you want to keep before you close the Earthlink account. I’m sure earthlink has a web-access page that you can get to from your alltell (you don’t have to use Earthlink’s e-mail application) to access your e-mail.
If nothing else, you’ll want to grab your address book so you can tell all your contacts your new e-mail address. (I made the mistake of switching and not telling quite everybody, so I “lost” some contacts).