Firstly, a codec is an "encoder/decoder", hence the term codec. This is the software used to package your voice conversations and send them over the Internet.
We allow only the following codecs: G729, ulaw, and alaw (G711).
Our preferred codec is G729 because it offers the highest compression and works on all internet connections, however G711 is available and generally used, because it offers the highest speech quality of any available VoIP codec.