yes i used one from http://asterisk.hosting.lv/ also this year DIGIUM paid codec is free since patent pending protection is finished,also its very obsolete since HD G722 codec and G711 are on demand,
You must not mix silence supress algorthm with newer codec G722 and G711 since it can cuttoff the sound when you speak and destroy call quality ,
G729 is still very popular when you use bad internet connection i hope Issabel developers can improve also this codec to be used in every new distribution of PBX issabel ,