I would like to redirect 911 calls from a lobby phone extension to a security officer's cell phone. Any idea how to accomplish that?

You might want to check the laws in the state to make sure that's legal. Otherwise you are looking at building some f-route tables and building some COS for those tables to redirect 911 calls ONLY from that one one.

I see a lawsuit coming.
911 should always go to public Law Enforcement.

Like CT said, F-routes are going to be the way to go.

This is in a lobby? what happens when a woman runs in off the street trying to avoid being assaulted by a rapist and calls 911 and the guy at the end of the cell phone is in a "no Service" area?

311 is help, can go anywhere. 911 is emergency, you want Security to heart attack calls?

Ok. I'll give you the whole scenario. The phone (actually there are 2) is for a 'teleboard' at an airport where there is a display with local businesses that provide services. Each business has a number that currently corresponds to a programmable key on an analog set. The set is on a POTS line and each of the 20 programmable keys are speed dial keys with the local business's phone number. I can no longer find this model of phone that is reliable to retain the speed dial numbers. (Eg. they press the 6th button for a taxi business and get nothing or they get the hotel who's number is stored under speed dial key 14.) So the customer often has to reprogram each speed dial key. The dial pad is covered by a wall mount bracket to prevent someone from stealing the set or using it to make any calls.
I am considering different solutions. One is to replace each set with an analog set that is an analog ext of their PBX, have them dial a speed dial access code (#2, its an NEC SV8100) and then the number of the business (which would be a speed dial bin). I would need to leave the dial pad accessible and could disable outside calls via a COR. But the customer does not want to allow callers to dial 911 because they don't want prank calls. A security office is always available so I thought I might approach the cust with sending 911 calls from the set to the sec officer's cell. But you've convinced me that that is a bad idea.

I think I've just talked myself into using a 24-button digital set and making a dial pad guard so the user just presses the appropriate DSS key but can't access the dial pad. I was trying to avoid making the dial pad guard because it is a pain to build. Thanks for your help.

Wander over to Viking Electronics and look at the K-1900-9 dialer. Since this is an intercom extension, you can easily program the (up to) 32 digit number in a speed dial bin and you don't have to do anything to the phone.

Carl

You can even beat $100 if you shop carefully on eBay.