Yahoo Messenger with Voice: Not your average instant messaging service, Yahoo Messenger with Voice offers free PC-to-PC calls around the globe, requiring only the Yahoo Messenger with Voice program, microphone and speakers (or headset). Users can leave voice mail for each other and check their call history to see all incoming, outgoing and missed calls, too. Users can also drag-and-drop photos into IM windows. The program also offers custom ring tones, file sharing and contact cards.

Yahoo Mail: A free email service, featuring a calendar, address book, and mobile access. Yahoo Mail includes ads throughout the email interface.

Other players include
Messenger:
AIM, MSN Messenger, Google Talk, Trillian

Mail:
Gmail, Hotmail, Netscape Mail

VOIP:
Skype, Vonage

What it could mean for marketers
Communication is shifting more and more to online, giving marketers the change to reach an audience where they already are and where they're going.

Yahoo offers themed backgrounds that appear directly in the instant messaging window called "IMVironments." Currently, the top five themes are from Shrek 2, baseball sponsored by GMC, Pop Tarts French Toast, Garnier Fructis and of course, Britney Spears. These skins are the perfect opportunity to reach some of the internet's most active instant messagers-- teens!

These themed backgrounds not only put your brand in front of potential consumers, but they build a consumer experience and loyalty with your brand.

Brands can also consider submitting ads to Yahoo to appear in the Yahoo mail interface.