I have an AsteriskNOW server setup w/ a Sangoma A200 FXO card (2 analog phone lines going into it). I’m wondering if anyone can help point me in the right direction. I have 6 Polycom 331 SIP phones attached to our network and I’m wondering if its possible to make it so when I put a call on hold, they can go to another phone and select the line they want to take off hold, rather than be required to transfer the call to each extension. I dont think its that big of a deal to do it that way, but the office i set this up for seems to think thats ‘too hard’ 
Any ideas?
With recent versions, you should be able to hijack a channel using ChannelRedirect(). This involves the hairy area of masquerading, so is relatively high risk for stability. I can’t remember whether there is any way for the dialplan to verify that the target channel is actually re-invited to a held SDP state.
The standard feature for doing this is Park. The target device dials a code which holds the call within Asterisk, rather than within the phone, and announces a dynamically created extension number (low 700s, by default) that can be used to retrieve the call. See features.conf.
hmm I’ll look more into Park. I had one idea–tell me if you think this would work: is it possible to have more than one SIP phone register with the same extension? I’m wondering if i can set up every phone in the office on 2 extensions (1 per line) and pretty much make it so it would practically act like a completely analog system in that if you pick up the phone in one room, and pick up the phone in another (Assuming you selected that line,) you would essentially have two phones off the hook on the same call. Is this what park does?
Plan 1 analogue systems aren’t designed to allow internal communication.
Asterisk can ring all the phones at once, but only the one that answers will be connected. (Dial(device1&device2&device3…)
Phones do not register with extensions; they registers as devices. An “extension”, in Asterisk terminology, may be associated with any number of devices, and a device may be accessible by any number of extension numbers. However, only one device can register as a particular device identity at any one time.
A parked call is not connected to any phone. Parking is a fairly standard PABX feature, so you should be able to find good explanations on the web.