iWAPu
This wireless instant-messaging service from Strategy.com offers real-time communication anywhere, anytime, through wireless, Internet-enabled phones.
WAP URL: http://www.strategy.com/
Web URL: http://www.strategy.com/

Office Servant
Offers POP3 access from cellular phones. Additional features available with registration.
http://ofsv.com/

Onebox.com
Use this service to respond to, send, and forward voice-based emails. Instead of a text message, recipients will get an email with an attachment that's actually your voice. You can also organize your faxes and voicemail.
WAP URL: http://wireless.onebox.com/
Web URL: http://www.onebox.com/

PhoneFish.com
This is another service you can use to access email from POP3 accounts on a Web-enabled phone. There are two flavors of service: Basic is free and is limited to one email account, and Premium gives you access to unlimited email accounts but has a monthly fee.
WAP URL: http://jgjg.com/
Web URL: http://www.phonefish.com/

TagTag
Provideds email, and pop3 access, as well as a PC based site builder.
http://www.tagtag.com/

wapMX.com
Allows users to check POP3, Yahoo!, and Hotmail accounts.
http://www.wapmx.com/

WappyMail
Allows users to check, send, reply to and delete mail.
http://www.wappymail.com/wap

Webcab SendMail
Allows users to access email.
http://webcab.de/sm.wml

Webcab World Wide Mobile Mail
Allows access to POP3 mailboxes from any WAP-capable device.
http://webcab.de/wwmm.wml

Yahoo! Mail
Free "you@yahoo.com" email.
http://mobile.yahoo.com/mail