User Agent Profiles (UAProf), such as that for 6120, are machine readable file formats that describe the capabilities of the phone. They are used by developers and on line service to help identify a device and look up its capabilities.
There's no other public information about the 6120, but such User Agent Profiles typically appear only shortly before the device in announced (typically 3-4 weeks). However it is worth noting that the information in User Agent Profiles is not always accurate and the files are sometimes updated after the official announcement.
Given the similarities to the UAProf of the 6110 Classic to the 6120 it is likely part of the same device family.
As with other recent models Nokia is recycling a device name. The original 6120 was a TDMA Analog version of the 6110.