Add VoIP extension to existing PBX

I’m looking to see if there’s a way we can pull this off. We’ve got an existing PBX with some extra extensions we’d like to make into cordless extensions that employees can forward their desk phone to and ‘rent’ them out when they go out in the shop. The problem is that we’ve got 4 buildings and all are tin cans so the signal wouldn’t penetrate them very well. What I have proposed was getting some WiFi phones like the Prestige 2000’s and setting up a few access points around the campus using the existing computer network. If it makes any difference, the PBX we are using is an old Inter-Tel Premier system, which may soon be upgraded to an ESI IVX E-Class system.

Now for the big question, would it be possible to set up Asterisk as a PBX to VoIP converter for 4 extensions like this? I was figuring on using some FXO cards from the extensions on the PBX but the big snafu I’m running into in my mind is that if someone does a blind transfer on the PBX and nobody answers the phone, how do I get it to ring back in the PBX. Can I set up Asterisk to not go ‘off-hook’ on the FXO card until the WiFi phone answers?

Also on a side note, are there some WiFi/SIP phones with a ‘flash’ key or someway to get Asterisk to trigger a hook-flash on the FXO card from a WiFi phone?

Also, can anyone suggest a durable WiFi/SIP phone that we could use for this, some of the guys that would be using this aren’t exactly ‘gentle’ with the phones around here.

Benjamin Jennings

Stay away from the zyxel phones they are extremely bad. (and they don’t do roaming).

It might be better to look for a simple ATA with a good dect phone. (have a look at the site of bang and olufsen, they have something that does roaming).