I actually bought one and tried it. I have to say that the dang thing works. I have a Blackberry 8700g with T-Mobile service. The service is quite splotchy in spots. It does seems to help on signals that use to drop to 2 bars and below. I cannot tell you how or why it works or if it really does. Only had it a few days but I seemed to notice a difference.
Here is what I would suggest if you get one (they are $1.99 or less). If you know there is an area that you hit driving to and from work each day where normally you have static, call your home land line and leave a long voice mail. When you get the antenna, install it and then do the same. See if you do not notice a difference. I honestly did.