Check with Frontier, they may offer a mail only plan for a few dollars a month. Most ISP (many, some, whatever) do. If they do you can keep the mail and slowly get everybody moved over to whatever you pick.

In most cases, switching between pop and imap is just putting in the settings. Depending on what your mail client is, you may need to set up both, and don't have the pop one check for mail anymore, as all your current mail will be stored and may be deleted when you remove the account.