Mailing lists are the main communication place for the community. Before asking questions there, you should search in the archives if somebody did not already solve similar issue. It sometimes happen that some version has well known problems which was faced by many users.
To post a message to the mailing list, you need to be subscribed. While posting a message, please try to describe well your problem (basically you should follow same rules as when reporting a bug), avoid sending HTML mails and do proper quoting of replies, so that it is easy for others to follow the discussion.
Sometimes you can not expect immediate answers on the mailing list, so please be patient. People might be on vacation or simply busy with other things. Reposting the same message again to the mailing list or directly to authors will usually not give you faster answer, it might just upset involved people.
You can also ask related questions on Stack Overflow.
The main list where the discussion is being held is firstname.lastname@example.org. It's just generic place where users or developers can discuss anything related to Gammu (this includes Wammu or third party frontends like Kalkun).
In past, there used to be some problems with licensing of some code in Gammu and separate lists for this purpose has been created - email@example.com. It is not much used nowadays, but should you find any legal problems with Gammu, please use this mailing list.