asterisk users - Aug 2006 - Question about 7940s and call forwarding

Hello, I need some advice on the following problem I'm trying to solve:

At the office we are using 7940s as our phones, connected to an asterisk
box via SIP. Pretty standard setup, nothing fancy. Everyone has an
extension that comes out as a single line button on the phones, with the
second line unused at this point.

Certain things on our phone system are set to ring all the phones in the
office (support queue fills up, etc.). I just simply do something like
this:

Dial("SIP/123&SIP/456&SIP/789")

which works just fine, except if someone wants to use the phone's
built-in call forwarding to send their calls to their house or cell
phone. Then, any call that rings all the phones gets picked up and
forwarded by that person's phone and they end up getting all the calls.

Originally I had set up everyone as agents and let them forward their
extensions anywhere, but the agent callback stuff makes things really
unstable, plus it's cumbersome to use compared to using the phone.

The solution I'm considering is to make the "ring all" calls ring
to the
second line button on all the phones and disabling call forwarding in
sip.conf for those lines. I'm just not sure how a phone set to forward
calls will react...will it properly not answer the calls on this line,
or will it try to forward them and fail and cause the calls to get
dropped? Will call transfers still work for calls that came in on the
second line?

Also if there's a better way of doing what I want to do I'm all ears. :)

-- 
Joshua M Thompson <funaho@jurai.org>