It's a pretty good phone. The sound is very good. I had to switch from my house line to the X at one point I the X sounded better. Maybe a little awkward to hold due to it's width, but the hump actually helps me keep a good grip on it.
I've occasionally had volume issues where it's hard to hear through the earpiece and once I had a strange tinny rattle during a call (sounded like a blown speaker). Both problems seem to have stopped, but I've heard others have similar, but more persistent, issues.
I'm not happy with the speakerphone at all the once or twice I tried to use it. Not a big showstopper for me. It works in a pinch.
Bluetooth headset support blows. I hate it. This is my biggest problem with the phone. The voice command system is slow to respond and often hard to hear (it seems to constantly set it's volume down too low, what is it with the phone and volumes?). It also is incompatible with the password lock screen, meaning if my phone is locked bluetooth doesn't work. I basically have to disable the lock screen completely (using a 3rd party app) before getting in the car. I'm hoping 2.2 fixes this.