More likely, and I will have to test this later today, your phone does not have USB Mass storage profile but Media Device profile.
My Motorla phone worked great with the Volt in that the Volt could read all my music. It also played well with the bluetooth that it displayed the caller ID and read the phone lists for numbers.
My new Samsung Galaxy Note 2 does fine for pairing and voice calls but doesn't do caller ID or phone lists

It also does not have USB mass storage any more, just Media Device profile. Which at least for Windows computers isn't a big deal as it still mounts the drive and lets me use it like a mass storage device. But it won't work with other computers like my Chromebook and I suspect maybe the Volt.
I will try plugging in my phone to the Volt and see if that is the problem.
Also, another way to debug it is to put some files on a USB stick and plug it in the Volt. If it reads them OK then the problem isn't the volt.