Number of POTS line for 1,500 users SIP Trunking site

[news2010a]

Hello,
Imagine I have one single site with 1,500 Cisco IP Phones 8941 users served by MPLS and SIP Trunking.

The WAN router is a C3945E with total of 12 FXO ports.

Let's say the WAN link/SIP Trunking goes down.

Question:
Since I don't think it is feasible to pay too many POTS lines or PRIs (otherwise the savings with SIP Trunking would be unjustified), is it a good idea to limit those 12 POTS lines only to desginated users (or phone numbers)?

That way in case an outage in SIP Trunking, designated security staff could make phone calls and call 911 or other services? Is that a good idea?

[Chris Deren]

Sure, better than no backup at all.

HTH,

Chris

[Robert Thomas]

Hi,

It sounds interesting. You could also look into implementing MLPP for call preemption in case of an emergency.

Also you could look into having a backup PRI with at least 24 channels for backup in case of an emergency.