I used to sell some of the wilson products for cell phones and got alot of postive feedback from my customers using thier antennas they can give you about a 10-15 db gain. As long as you have the Proper adapter for your phone. The adapters for nokia phones are the ones that velcro on the back of your phone arent that effective at all. Also having an antenna plugged in can increase the life of your cell phone battery since it has to work alot less trying to find signal. If you really want a bigger gain in signal you can also buy a 3 watt amplifier for your external ant from wilson as well... These are kind of pricey about 300 bucks... but the average phone is about 1/2 watt of power ... I would check out what they have to offer for your phone at
www.wilsonelectronics.com before buying some knock-off ebay crap..