The following is excerpted from Tom Keating's blog on TMCnet. Since I doubt he will post it here directly, I'm copying over the pertinent part of his request. The full text of the article can be found here:
He is talking about a Nortel patent for call screening on the PSTN, but then makes these observations:
..... Yeah, no kidding 'call screening' is a desirable feature! What's even more interesting is the patent diagram makes no mention of VoIP, as seen here:
[omitted, see above link|Diagram]
The text of the patent itself makes no mention of VoIP, so this is strictly traditional PSTN hosted voicemail call screening. Earlier today I griped about the lack of real-time call screening in VoIP services, such as Vonage & Packet8. It's not that hard, especially if using software. You should be able to easily setup a 3-way conference call via SIP to enable call screening. That is, one leg is the caller, the second leg is your phone, and the last leg is special call screening software running on your PC. You just send a SIP Invite to the PC, have the software auto-accept the SIP invite and connect legs
FREEPBX-2& FREEPBX-3. If the user accepts the call, simply connect/conference leg FREEPBX-1.
Now most people don't want to perform call screening on their PC. Most would want to do it via the phone, especially since the PC may not be on or nearby. Well, that's easy enough as well. First, you ring the user's phone, then after X number of rings, the phone stops ringing and the hosted voicemail system prompts the caller to leave a message. Simultaneously, the hosted voicemail system calls the phone again (via another SIP Invite) and this time tells the phone to play a special ringtone to indicate a caller is leaving a message. Hearing the special ringtone, the user can pick up the phone, be conferenced into the voicemail message being left (with mic muted) and if the user presses a touch-tone they can instantly pull the caller out and their mic is unmuted. Simple!
Damn, between the "special" ringtone to indicate the opportunity to screen the caller and the "instant" ability to pull a caller out of a hosted VoIP voicemail system, I should patent these! The special ringtone can even work with analog phones connected to ATAs simply by varying the length of the ring voltage, i.e. two super-quick rings.
Only thing I would add to this is that there might be a desire for the call screening destination to be different from the original destination. For example, call comes into extension 1234, goes to voicemail, but now you may want to screen the call at any of extension 1234, another extension (Supervisor? Attendant? Another family member?), and maybe even at a cell phone or other phone external to the system. So the screening destination could be a ring group or follow-me, and in that case the distinctive ring may not be possible in all situations, thus it may be desirable to play a special tone of some kind before connecting to the audio path.
Just passing this along because I rather doubt that Mr. Keating will stop by here and make the request directly, and it does seem like a good idea for a feature.