To the best of my knowledge, there have been three versions of hardware and two firmware versions for the HG612. See .
The hardware revisions, in order of age, are Huawei Part Nos. 53030428, 53031385 (2V) and 53031504 (2B)
And the HG612 firmware is either the earlier V100R001C01B027SP06 or the later V100R001C01B028SP10.
The xDSL PHY driver is identical in both versions of the firmware, and line sync rates should be the same in all (faultless) versions, absent any relevant changes in the hardware.
For those with a spare modem to play with, unlocked SP10 firmware has been built. It can also be flashed into the earlier (SP06) HG612 hardware without a problem. 
I would interested to see inside a 2B, if anyone fancies cracking one open and taking a few shots...
There are four Philips screws retaining the top cover. These are concealed under the rubber feet on the base of the modem. To access the screws, the feet can be teased up using a knife. The feet don't actually need to be removed.
There is also a single concealed clip that should be pressed inwards before the top cover will release. The clip is located midway along the top edge that hosts the LEDs and the Openreach logo.
There are some very clear instructions on opening the Huawei at .
Edited by asbokid (Sun 04-Sep-11 01:21:54)