diff --git a/Makefile b/Makefile
index d4a52a26..c7111153 100644
--- a/Makefile
+++ b/Makefile
@@ -43,6 +43,7 @@ install:
 	install -m 755 src/${APP}-logging ${DESTDIR}${PREFIX}/bin
 	install -m 755 src/${APP}-addsipuser ${DESTDIR}${PREFIX}/bin
 	install -m 755 src/${APP}-rmsipuser ${DESTDIR}${PREFIX}/bin
+	install -m 755 src/${APP}-sipfreeext ${DESTDIR}${PREFIX}/bin
 	mkdir -m 755 -p ${DESTDIR}${PREFIX}/share/man/man1
 	install -m 644 man/${APP}.1.gz ${DESTDIR}${PREFIX}/share/man/man1
 	install -m 644 man/${APP}-keydrive.1.gz ${DESTDIR}${PREFIX}/share/man/man1
@@ -133,6 +134,7 @@ uninstall:
 	rm -f ${PREFIX}/bin/${APP}-logging
 	rm -f ${PREFIX}/bin/${APP}-addsipuser
 	rm -f ${PREFIX}/bin/${APP}-rmsipuser
+	rm -f ${PREFIX}/bin/${APP}-sipfreeext
 clean:
 	rm -f \#* \.#* debian/*.substvars debian/*.log
 	rm -fr deb.* debian/${APP}
diff --git a/src/freedombone-adduser b/src/freedombone-adduser
index 6e32160e..2e8b619e 100755
--- a/src/freedombone-adduser
+++ b/src/freedombone-adduser
@@ -205,6 +205,7 @@ if grep -q "Blog domain" $COMPLETION_FILE; then
 fi
 
 if grep -q "install_sip" $COMPLETION_FILE; then
+	SIP_EXTENSION=$(freedombone-sipfreeext)
     freedombone-addsipuser -u $MY_USERNAME -e $SIP_EXTENSION -p "$NEW_USER_PASSWORD"
     if [ ! "$?" = "0" ]; then
         echo 'SIP user could not be added'
diff --git a/src/freedombone-sipfreeext b/src/freedombone-sipfreeext
new file mode 100755
index 00000000..7a206e6d
--- /dev/null
+++ b/src/freedombone-sipfreeext
@@ -0,0 +1,69 @@
+#!/bin/bash
+#
+# .---.                  .              .
+# |                      |              |
+# |--- .--. .-.  .-.  .-.|  .-. .--.--. |.-.  .-. .--.  .-.
+# |    |   (.-' (.-' (   | (   )|  |  | |   )(   )|  | (.-'
+# '    '     --'  --'  -' -  -' '  '   -' -'   -' '   -  --'
+#
+#                    Freedom in the Cloud
+#
+
+# Returns the next free SIP extension number
+
+# License
+# =======
+#
+# Copyright (C) 2015 Bob Mottram <bob@robotics.uk.to>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+CONFIG_FILE=/etc/sipwitch.conf
+
+extensions=()
+
+# get the used extensions
+for line in $ (cat $CONFIG_FILE)
+do
+    if [[ "$line" == "<extension>"* ]]; then
+        ext=$(echo "$line" | awk -F '>' '{print $2}' | awk -F '<' '{print $1}')
+        extensions+=($ext)
+    fi
+    if [[ "$line" == '</provision>' ]]; then
+        break
+    fi
+done
+
+#echo "used extensions:"
+#echo $extensions
+#echo " "
+
+# which is the first available unused extension ?
+for ext in $(seq 201 299);
+do
+    is_used=
+    for i in "${extensions[@]}"
+    do
+        if [[ "$i" == "$ext" ]]; then
+            is_used=1
+            break
+        fi
+    done
+    if [ ! $is_used ]; then
+        echo $ext;
+        break
+    fi
+done
+
+exit 0