Just a comment really.
After going through 2 * WAG54GP2 devices, 3 * WAG310G devices I now have a SPA2102
I had to buy a SPA2102 about 18 months ago when there was no stock of the WAG310G.
Anyway, the SPA2102 has been playing up for a wee while, crackling line and poor performance.
I changed the power supply like a few people had mentioned and the call quality is back to perfect.
I could not believe the SMPS could do that, I would have thought there would have been another filtering cap on the device end to take away any PSU ripple and fluctuations.
Anyway if you are have trouble with the voice quality, try changing the power supply. It has worked for me.
What I would like to see is a dual / triple outlet PSU so I only have to have one pluged in that can feed the Modem, The ATA and the Switch.