I received a refurbished 8310 from ATT and the trackball barely moved. Instead of sending it back and waiting for a new one, I wanted to find a replacement trackball. Most sites had them for $20 - $60. Then I found this one on Amazon. I figured it was only $10 in case I got burned. But WirelessFinest came through! The trackball looks and feels brand new and it was delivered in 2 days! Highly recommended.