Way to do this? Avaya Telecommuter type mode?

I was wondering if anyone knows a way to do this with Asterisk 1.4.26. Previously, our I had an Avaya Definity G3si PBX where remote users were using Avaya softphones in telecommuter mode. This is the mode where the softphone registers to the IP PBX over VPN and you control the call with the softphone but the talk path is via your home/cell phone. This allows you to use your office extension and features (hold, conf, transfer) but you are not at the mercy of poor voice quality if your Internet connection is shaky.

I searched for it, but I’m not sure what to call it. Split call? Split mode? etc.

Anyone know how to have Asterisk do it? We have a guy that’s going to work a call queue and we need to make sure voice quality stays good. I was hoping he could control calls via SIP softphone but the voice would go over PSTN to his home phone. He could log on/log off the queue.

Another way would be to just forward the calls to his home phone but I don’t know how Asterisk would know if the phone is “busy” or not and would simply just transfer the call. Call hold times are up to 20 minutes for this guys particular knowledge.

Sorry in advance if I posted in the wrong place.