Index: channels/chan_dahdi.c
===================================================================
--- channels/chan_dahdi.c	(revision 278424)
+++ channels/chan_dahdi.c	(working copy)
@@ -2744,6 +2744,52 @@
 	p->subs[SUB_REAL].needringing = value;
 }
 
+static void my_set_polarity(void *pvt, int value)
+{
+	struct dahdi_pvt *p = pvt;
+
+	if (p->channel == CHAN_PSEUDO) {
+		return;
+	}
+	p->polarity = value;
+	ioctl(p->subs[SUB_REAL].dfd, DAHDI_SETPOLARITY, &value);
+}
+
+static void my_start_polarityswitch(void *pvt)
+{
+	struct dahdi_pvt *p = pvt;
+
+	if (p->answeronpolarityswitch || p->hanguponpolarityswitch) {
+		my_set_polarity(pvt, 0);
+	}
+}
+
+static void my_answer_polarityswitch(void *pvt)
+{
+	struct dahdi_pvt *p = pvt;
+
+	if (!p->answeronpolarityswitch) {
+		return;
+	}
+
+	my_set_polarity(pvt, 1);
+}
+
+static void my_hangup_polarityswitch(void *pvt)
+{
+	struct dahdi_pvt *p = pvt;
+
+	if (!p->hanguponpolarityswitch) {
+		return;
+	}
+
+	if (p->answeronpolarityswitch) {
+		my_set_polarity(pvt, 0);
+	} else {
+		my_set_polarity(pvt, 1);
+	}
+}
+
 static int my_start(void *pvt)
 {
 	struct dahdi_pvt *p = pvt;
@@ -3461,6 +3507,10 @@
 	.set_pulsedial = my_set_pulsedial,
 	.get_orig_dialstring = my_get_orig_dialstring,
 	.set_needringing = my_set_needringing,
+	.set_polarity = my_set_polarity,
+	.start_polarityswitch = my_start_polarityswitch,
+	.answer_polarityswitch = my_answer_polarityswitch,
+	.hangup_polarityswitch = my_hangup_polarityswitch,
 };
 
 /*! Round robin search locations. */
Index: channels/sig_analog.c
===================================================================
--- channels/sig_analog.c	(revision 278424)
+++ channels/sig_analog.c	(working copy)
@@ -530,6 +530,35 @@
 	}
 }
 
+#if 0
+static void analog_set_polarity(struct analog_pvt *p, int value)
+{
+	if (p->calls->set_polarity) {
+		return p->calls->set_polarity(p->chan_pvt, value);
+	}
+}
+#endif
+
+static void analog_start_polarityswitch(struct analog_pvt *p)
+{
+	if (p->calls->start_polarityswitch) {
+		return p->calls->start_polarityswitch(p->chan_pvt);
+	}
+}
+static void analog_answer_polarityswitch(struct analog_pvt *p)
+{
+	if (p->calls->answer_polarityswitch) {
+		return p->calls->answer_polarityswitch(p->chan_pvt);
+	}
+}
+
+static void analog_hangup_polarityswitch(struct analog_pvt *p)
+{
+	if (p->calls->hangup_polarityswitch) {
+		return p->calls->hangup_polarityswitch(p->chan_pvt);
+	}
+}
+
 static int analog_dsp_set_digitmode(struct analog_pvt *p, enum analog_dsp_digitmode mode)
 {
 	if (p->calls->dsp_set_digitmode) {
@@ -1266,6 +1295,7 @@
 		case ANALOG_SIG_FXOKS:
 			/* If they're off hook, try playing congestion */
 			if (analog_is_off_hook(p)) {
+				analog_hangup_polarityswitch(p);
 				analog_play_tone(p, ANALOG_SUB_REAL, ANALOG_TONE_CONGESTION);
 			} else {
 				analog_play_tone(p, ANALOG_SUB_REAL, -1);
@@ -1357,9 +1387,21 @@
 				p->owner = p->subs[ANALOG_SUB_REAL].owner;
 			}
 		}
-		if ((p->sig == ANALOG_SIG_FXSLS) || (p->sig == ANALOG_SIG_FXSKS) || (p->sig == ANALOG_SIG_FXSGS)) {
+
+		switch (p->sig) {
+		case ANALOG_SIG_FXSLS:
+		case ANALOG_SIG_FXSKS:
+		case ANALOG_SIG_FXSGS:
 			analog_set_echocanceller(p, 1);
 			analog_train_echocanceller(p);
+			break;
+		case ANALOG_SIG_FXOLS:
+		case ANALOG_SIG_FXOKS:
+		case ANALOG_SIG_FXOGS:
+			analog_answer_polarityswitch(p);
+			break;
+		default:
+			break;
 		}
 		break;
 	default:
@@ -2521,6 +2563,7 @@
 		case ANALOG_SIG_FXOLS:
 		case ANALOG_SIG_FXOGS:
 		case ANALOG_SIG_FXOKS:
+			analog_start_polarityswitch(p);
 			p->fxsoffhookstate = 0;
 			p->onhooktime = time(NULL);
 			p->msgstate = -1;
@@ -2702,6 +2745,7 @@
 					ast_setstate(ast, AST_STATE_DIALING);
 				} else {
 					ast_setstate(ast, AST_STATE_UP);
+					analog_answer_polarityswitch(p);
 				}
 				return &p->subs[index].f;
 			case AST_STATE_DOWN:
@@ -3440,6 +3484,7 @@
 		case ANALOG_SIG_FXOLS:
 		case ANALOG_SIG_FXOGS:
 			i->fxsoffhookstate = 0;
+			analog_start_polarityswitch(i);
 		case ANALOG_SIG_FEATD:
 		case ANALOG_SIG_FEATDMF:
 		case ANALOG_SIG_FEATDMF_TA:
Index: channels/sig_analog.h
===================================================================
--- channels/sig_analog.h	(revision 278424)
+++ channels/sig_analog.h	(working copy)
@@ -147,6 +147,14 @@
 	/*! \brief Set channel off hook */
 	int (* const off_hook)(void *pvt);
 	void (* const set_needringing)(void *pvt, int value);
+	/*! \brief Set FXS line polarity to 0=IDLE NZ=REVERSED */
+	void (* const set_polarity)(void *pvt, int value);
+	/*! \brief Reset FXS line polarity to IDLE, based on answeronpolarityswitch and hanguponpolarityswitch */
+	void (* const start_polarityswitch)(void *pvt);
+	/*! \brief Switch FXS line polarity, based on answeronpolarityswitch=yes */
+	void (* const answer_polarityswitch)(void *pvt);
+	/*! \brief Switch FXS line polarity, based on answeronpolarityswitch and hanguponpolarityswitch */
+	void (* const hangup_polarityswitch)(void *pvt);
 	/* We're assuming that we're going to only wink on ANALOG_SUB_REAL - even though in the code there's an argument to the index
 	 * function */
 	int (* const wink)(void *pvt, enum analog_sub sub);
Index: configs/chan_dahdi.conf.sample
===================================================================
--- configs/chan_dahdi.conf.sample	(revision 278424)
+++ configs/chan_dahdi.conf.sample	(working copy)
@@ -820,14 +820,22 @@
 ; useful to use the ztmonitor utility to record the audio that main/dsp.c
 ; is receiving after the caller hangs up.
 ;
-; Use a polarity reversal to mark when a outgoing call is answered by the
-; remote party.
+; For FXS (FXO signalled) ports
+;   switch the line polarity to signal the connected PBX that an outgoing
+;   call was answered by the remote party.
+; For FXO (FXS signalled) ports
+;   watch for a polarity reversal to mark when a outgoing call is
+;   answered by the remote party.
 ;
 ;answeronpolarityswitch=yes
 ;
-; In some countries, a polarity reversal is used to signal the disconnect of a
-; phone line.  If the hanguponpolarityswitch option is selected, the call will
-; be considered "hung up" on a polarity reversal.
+; For FXS (FXO signalled) ports
+;   switch the line polarity to signal the connected PBX that the current
+;   call was "hung up" by the remote party
+; For FXO (FXS signalled) ports
+;   In some countries, a polarity reversal is used to signal the disconnect of a
+;   phone line.  If the hanguponpolarityswitch option is selected, the call will
+;   be considered "hung up" on a polarity reversal.
 ;
 ;hanguponpolarityswitch=yes
 ;