There is some docs written. It isn't quite as good as it ought to be, but it is still better than nothing.

Start off with the README that includes full details on how to write a syntacticly correct config file.

When you think you're starting to understand some of it, try the example config file and see how some easy things are done.

For those weak-hearted who thinks regexes are tricky, I have this regex guide that explains some of the weird letter combinations you might wanna use!

To figure out the command line options to mail2sms, have a look at the web version of the man page.

For detailed information about what has changed between versions and releases, have peek in the CHANGES file...