Cannot use autoconf: http://sourceforge.net/p/opalvoip/feature-requests/18/

Index: plugins/Makefile.in
--- plugins/Makefile.in.orig
+++ plugins/Makefile.in
@@ -41,6 +41,16 @@ DEFAULT_SOUND	= sound_pulse
 endif
 endif
 
+###################################SNDIO
+HAS_SNDIO      = @HAS_SNDIO@
+
+ifeq (1,$(HAS_SNDIO))
+SUBDIRS += sound_sndio
+ifeq (,$(DEFAULT_SOUND))
+DEFAULT_SOUND  = sound_sndio
+endif
+endif
+
 ###################################ESD
 HAS_ESD		= @HAS_ESD@
 
