diff -r f38380784cd3 -r 7f174345ae9a data/dictionary.xml
--- a/data/dictionary.xml	Mon Aug 19 16:40:02 2013 +0200
+++ b/data/dictionary.xml	Mon Aug 19 16:53:20 2013 +0200
@@ -2586,6 +2586,29 @@
 		</explanation>
 	</concept>
 	<concept>
+		<term abbreviation="PBX" completeForm="private branch exchange" language="en"/>
+		<explanation language="en">
+			<text>
+				a kind of telephone exchange used in some office or company for its own purposes;
+				provides FSX interface for connected phones;
+				can have FXO interface for connecting to PTSN (for calling outside the company);
+				nowadays are often deployed digital VoIP PBXes based on free software like Asterisk;
+				such telephony can be pure IP based with no POTS or can have some FSX or FXO interfaces
+			</text>
+		</explanation>
+	</concept>
+	<concept>
+		<term abbreviation="PSTN" completeForm="public switched telephone network" language="en"/>
+		<explanation language="en">
+			<text>
+				the worldwide public telephony network consisting of networks of particular carriers;
+				the network is developed according to ITU-T standards and recommendations
+				and uses uniform system of telephone numbers based on ITU-T recommendation E.164
+				which provides a single global address space for telephone numbers
+			</text>
+		</explanation>
+	</concept>
+	<concept>
 		<term abbreviation="POTS" completeForm="plain old telephone service" language="en"/>
 		<explanation language="en">
 			<text>