The S10 and S11 use the same amplifier base, but they come with different styles of headsets. The S10 headset is convertible and can be worn around-your-ear (earloop style) or over-your-head (headband style). The S11 headset is a simple headband style.
The S12 is the newer version of the S10. Both include the same convertible headset, but the S12 amplifier is updated with a newer look and feel. The new S12 base does not include a tone controller.