Cingular Wireless, Sprint Nextel and Verizon Wireless are starting a service that will allow users to post messages on Facebook’s home pages or search for other users’ phone numbers and email addresses from a cell phone.

In all, an estimated 300 sites, including smaller ones such as Study Breakers for high schoolers and Photobucket, a site for posting images, make up the social network universe.

Wharton marketing professor David Bell says the long-term success of these sites will depend on their ability to retain the interest of their members.

Single payments for regional advertising of profile (one-time appearance in scrolling banner for $1 – user picture, link, short text for mouseover; bidding war for stationary second banner cost of $1/minute).

Yes/No; While it is free to use, POF offers premium services as part of their upgraded membership, such as seeing the date and time a user viewed your profile and allowing you to see whether a user read and/or deleted your message.

Popular social networking sites, including My Space and Facebook, are changing the human fabric of the Internet and have the potential to pay off big for investors, but — given their youthful user base — they are unusually vulnerable to the next ‘new new’ thing.

As quickly as users flock to one trendy Internet site, they can just as quickly move on to another, with no advance warning, according to Wharton faculty and Internet analysts.

Facebook just received an additional million in venture capital.

Both companies are planning to extend their reach beyond the computer screen to cell phones.

All Paid users can message and post and they also have added benefits.