Thanks to the User Agent Profile lists on Nokia.com we know there is another S60 device on the way. The 6120 runs S60 3rd Edition Feature Pack 1 (Symbian 9.2), is a 3G device (including HSDPA) and has a QVGA screen. The device is referred to as the 6120c indicating its full name will be the Nokia 6120 Classic.
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.
All we know about the Nokia 3109 Classic from the XML file is that it will run under the Nokia's S40 platform, and will have a screen resolution of 128×160.