A full replacement of their existing switch was out of the question for budgetary reasons.  So integration with the Partner II was proposed.

We configured an Asterisk server with 3 - X100P analog line cards from Digium, to provide dial tone to an asterisk server.  One of these cards connected to a POTS phone line from Qwest.  The other two cards connected to two available ports on the Partner II.

The school had been wired with Ethernet many years back, so Ethernet IP phones were easily added to existing outlets in classrooms.  To keep costs down, Grandstream Budgetone 100 IP phones were used in the classrooms.  These phones provided the basics (VM Message waiting lamp, Caller ID, Transfer Button, Hold, etc.) for a great price.  However, we did experience some pushback with the overall 'feel' of the phones as they are fairly lightly built and cheap feeling.  We ended up switching one of them out for a Uniden UIP200 for one user who was very unhappy with her Grandstream.  The Uniden is a much better phone, but also costs about $50 more.  A Grandstream Handytone ATA adapter was used to connect an analog cordless phone to the Asterisk server.  In hindsight, I would have preferred to use a Sipura ATA in this application, but the Handytone worked fine.  It just has less options and features than a Sipura for about the same price.

In order to integrate the Asterisk server with the Partner II, we created a hunt-group on the Partner II, which included the two ports we were using to interconnect the systems.  On the Asterisk box, we created a 'trusted' IVR context to receive inbound calls from the Partner II.  This allows the receptionist to transfer calls from the Partner II to a classroom on the Asterisk box by using a two-stage dialing process.  She hits 'transfer' on her Partner II phone, then dials the number for the Asterisk hunt-group.  The Asterisk IVR answers this line and the receptionist then enters the classroom extension number and completes the transfer. 

Outbound calls are routed via the first available line.  In the case of the lines that are interconnected with the Partner II, this involved an automated two-stage dialing process.  When a classroom dialed an outside number, the Asterisk system would open a connection to the Partner II, dial 9 to reach an outside line on the partner, pause, then dial the requested number.  This worked fine, but it did create a lag in connecting the user's call that took a bit of getting use to for the staff.  A side benefit of this interconnection was the ability to easily dial Partner II extensions from the Asterisk box.  We created a dial '8' prefix that allowed Partner II extension to be dialed.  For example if a staff member wanted to call extension 41 on the Partner II, they would dial 841 from an IP phone.  This worked well, and connection times were fast compared to accessing an outside line through the Partner II.

Parents or spouses of staff members wishing to reach a teacher directly could call into the system using the Qwest line.  This line was answered by an IVR menu that routed calls to classrooms after class hours, but transferred calls to voicemail during class so as not to disturb the classes.  An automated staff directory was provided on this line to allow for easy call routing.

Overall the installation went as expected.  However several weeks after the installation 'red alarms' started to appear on one of the X100P cards connected to the Asterisk box.  These alarms would clear if one disconnected the line and then reattached it.  But the alarm would return within several minutes.  We puzzled over this behavior for several weeks.  We replaced the X100P cards, cables… Everything we could think of.  In the end, it was a setting on the Partner II related to voicemail MWI.  Someone had managed to leave a voicemail for the extension of one of the ports we were using to interconnect to the Asterisk box.  This led the Partner II to signal that a message was waiting for the extension by oscillating the voltage on the port, which confused the X100P and caused the red-alarm.  Once MWI was disabled on the Partner II port everything functioned perfectly.

Early on, one complaint that we encountered was echo on the line, when placing calls outside the school.  The problem seemed to appear only on calls going out over the dedicated Qwest line.  Adjusting the echo training and RX/TX gains on the effected X100P card mitigated the problem to a great extent.  Echo was never a problem on the ports interconnected with the Partner II switch.

In the end, the expansion using Asterisk was a resounding success.  The school achieved its aim of adding phone service to the classrooms with minimal cost and no rewiring.  I see great potential for Asterisk in schools as it provides a feature rich platform for delivering telephony services as a price schools can afford.  Its powerful scripting environment allows for very customized dial plans and provides flexibility when integrating with legacy systems.