Are you saying that when you're having a conversation on a land-line phone, your GSM BlackBerry will cause interferance that both parties can hear?
If that's the case, then I misunderstood. I thought you were talking about hearing interferance on your BlackBerry during a voice call on your Blackberry. My bad!
I'm on the phone a lot at work, so I have a corded headset. If my BlackBerry is within a foot or two of that cord, it will cause interferance that I (and whomever I'm talking with) can hear. Verizon tech support gives me crap about it all of the time.
On the other hand, if I use the handset, it picks up no interferance from the BlackBerry, even if it's only a few inches away. Neat.
I'm still a huge GSM fan. Seems to be a much larger selection of phones (i.e. when will there ever be a CDMA 7100 series BlackBerry???) that are less expensive, and you can buy them from other places BESIDES your CDMA carrier.