i have a z2. I bought a unlocked z2 hard drive off ebay. I think it is a toshiba 60gb. I'll have to take it out to verify it. He sent me an email offering a z3 upgrade for 50.00. I can't tell a difference between the two. I can do voice commands, but I keep hearing people say you can change the track or song by voice command. What is the CDDB?