I'm assuming you're referring to the 'Call Phone' feature recently added to Gmail.
While I haven't yet tried it 2-way under Linux, I have played with the Gmail 'Call Phone' feature under Windows. If you don't have a Voice account tied to your Gmail account, the CID comes arcoss as some random phone number. However, if you DO have a Voice account and number, your CID will show as that number. Likewise, if you set your Voice options to forward to Google Chat, you will receive a pop-up for calls coming in on your Voice number. (It was actually kinda neat when I tried it. My cell started ringing and, at the same time, I got the 'incoming call' pop-up.) I don't presently have a Linux box at home (aside from my little file server), but I do use Linux at work and I did try to call my GV number to see how well it worked. While I didn't have a mic, I was able to hear clearly (albeit with a small delay, probably network) with a set of headphones.
