Speek currently had has no formal scheduling mechanism, but we are looking to add this at some point in the future. Your line is always open for use, just like a traditional conference line.
For scheduling, using a third party calendar program while copying and pasting your Speek link works best. You can even copy and paste your Speek link into an email with a more formal invite. At the time of your call, those you've invited will choose their methods for connecting, and then be on the line. It's as simple as that!