Generally spoken, all clients can be used for callback connections. You can even use an ordinary terminal program like minicom to connect to a callback server. The only thing you have to do is to tell your modem to AutoAnswer the phone when a RING is detected by the modem. This means that the modem will pick up the phone after one RING . Remember, this is done without any client software interaction.
Some servers use a special login program therefore.
The kppp setup Setting up kppp to connect to a Linux callback server is quite straight forward. See the troubleshooting section if you are confronted with trouble. Think about your server a moment. Use CR as your line termination. Have a look on what the server asks you so you can write your login script afterwards.