Actually, I *have* seen call transfer like Vonage, from the VoIP
company that did it first: VoicePulse (http://www.voicepulse.com/).
In the last three or four months, VoicePulse has introduced several
new and innovative features, and call transfer just happens to be one
of them. Once VoicePulse had introduced the feature, Vonage customers
apparently started requesting it, and when Vonage implemented it they
even used the same code (90#) to initiate the transfer. I'm not
saying VoicePulse was the first to ever do something like this, but
Vonage *definitely* wasn't the first.
I've been watching the VoIP scene develop for the past few months and
one thing I've noticed is that among the "big three" VoIP providers
(VoicePulse, Packet8, and Vonage), VoicePulse looks to be the clear
leader in features now, and is even a bit less expensive than
Vonage. I think the only reason they aren't the larger company is
because they have numbers for incoming calls in relatively few area
codes. But that said, just a few days ago they announced that they
are offering numbers in the 212 area code in New York City. Somehow,
I have a feeling those are going to get snapped up rather quickly!