Sign up now and set up your HTTP gateway with clickatell. Then you'll be able to configure SmsRc to use your account: just press the Configure button on the main window and enter your account's properties.
The clickatell feature of two-way messaging is now supported, since v.1.55 (its support still considered experimental). Note that you don't need a two-way messaging account for your two-way service. SMS Reception Center is unique as it may receive messages via a GSM modem and send them via Clickatell simultaneously. You will get incoming messages at your local provider's price (it's usually ZERO) and send outgoing messages with the clickatell's price and speed.
If you want message recipients to be able to answer, the From phone parameter in SmsRc gateway settings must be set to the international phone number of your phone or modem.