A free Classmates.com account gives you access to only a few features. You can create your profile and deck it out to your heart's content. You can also look at the profiles of fellow users. And you can participate in group discussions on message boards. But after that, your options begin to dwindle.
If you want to be able to send messages to fellow members, you'll have to upgrade to a Gold membership. To leave a message on another person's public bulletin board requires at least one of the two of you to have a Gold membership. You can designate your location on a map with a free account, but to view anyone else's location you'll have to pay for a membership.
Other Gold membership features include event-planning tools. Using these, you can create invitations for gatherings and reunions. You can also see the names and messages left by people who have visited your profile. A Gold membership gives you the option to build a private photo album and message board, too.
In many ways, the membership structure of Classmates.com resembles an online dating service more than other online social network sites. Sending messages on other services is usually free to all members. But many dating sites require users to pay for a membership before they can actually make contact with other members.
If you do upgrade to a full membership, you'll be able to take advantage of all the features. You'll have the ability to contact other members and organize events. However, these features will be somewhat limited depending upon the account status of the people you try to contact. Some may create a profile only to abandon it later rather than upgrade to a full membership.
Having to pay to access basic features might annoy some users. But that's just one of several complaints that some people have aimed at Classmates.com.