Disable call waiting

[kjaslow]

I'm using a W60P with W56H handsets. It's a new setup and I'm hoping I'm just overlooking something. With my previous phone (and any phone I've ever used), I could dial *70 prior to dialing a phone number to disable call waiting just for that call. I see that menus exist to turn call waiting on or off, but the beauty of using *70 is that it could be added to the number in the directory. I've been unable to make *70 to work on this phone. If I just send the number as *70xxxxxxxxxx (in the US, where I use real numbers where I've typed an 'x') the number is not accepted by my ITSP.

If I just dial *70 and send on the Yealink, my provider gives back the tone I get when the number was invalid. With any other phone, I would get back a dial tone at this point.

Anyone have any ideas how to make this work?