FastMail supports WAP at http://wap.fastmail.fm/.
You can access the beta WAP service (sometimes used for testing new features) at http://wap.fastmail.fm/beta/.
Log in with your full email address and password (you can replace the '@' with '=', '/' or '#' if your phone doesn't support entering @). Alternatively, use 'wap.YOURDOMAIN.EXT' as the hostname and just use your username, the same as with web.
You can create a bookmark to log you in automatically as follows:
NOTE: While guests can use this service to view email, they can not send. This is a technical limitation caused by the fact that the WAP software uses the regular SMTP servers.
NOTE: The WAP server supports https, but uses a self-signed certificate, so you will certainly get complaints from your phone about the certificate being used. Unless you use 'wap.fastmail.fm' you will also get a complaint about the name not matching, and some phones will refuse to communicate securely at all.
NOTE: If you enter your username or password incorrectly you will get PHP's totally insane error message "too many failed login attempts" error. This really just means your login details were wrong. Please check that your phone is not automatically capitalizing the first letter of your username or password.