Hi,
I've got Vonage as well, and I also want to transfer to my cell phone when they press 2. I just figured out how to transfer the call yesterday....
On Vonage, to transfer a call, you press flash, then #90, then the # you want to transfer to.
In IVM, go to Settings->Transfer Settings, I forget what the label has on it, but in the edit box it will have "!," in it. Change that to "!,#90" for both Blind Transfer settings.
In your OGM, set the key press action Detail to Blind Transfer & the your cell # it'll do the transfer. When it transfers your cell gets the caller ID of the caller.
The drawback as far as I can tell is that you can't do a Confirmed Transfer when you do it this way. If you don't answer it, it'll go to your cell phone's voicemail.