"What about SIP/VoIP support in 6120? Is it built in?"
There is a SIP settings menu, but I didn't have the chance to test it with VOIP.
"I find WiFi is almost a necessity now however, so that lets it down a little. I agree adding these features adds to cost and this is quite a breakthrough device at the price so I can't really complain."
That's the thing to bear in mind, this is a model for a much more mainstream audience, I think it's meant to make S60 a more viable proposition for people who currently don't buy smart phones.
At the moment most phone users don't use wifi, so including it would have made the phone unnecessarily expensive for its target audience (and a bit more bulky and heavy too). The same goes for 5mp cameras, TV out etc, they'd be nice but they'd turn this into a completely different phone.
I suspect wifi (or perhaps wimax?) may well become a standard feature in most future phones though, even on cheap models, just as Bluetooth has become. Nokia and various other major manufacturers have said they're already doing wimax handsets right now, which will hopefully get the phone network operators worried.
"I think Nokia not supporting USB charging is really slack."
They've only just started supporting standard USB cables at all, most models in 2006 still used the proprietary Pop-Port standard! The current situation is huge progress on where they were (Pop-Port cables and adaptors were very expensive compared to USB cables), although as you say they ought to be giving people the option of ordinary USB charging as so many other devices do.
With the 6120 though, I would say it's worth bearing in mind that most ordinary phone users don't charge their phone through a computer, and it's ordinary users that this particular model is aimed at.
"but it's a wireless world and I use a laptop exactly becuase it has no wires and I can be comfortable while I use it all day."
It is a wireless world, but if we're just talking about the foot or two between your phone and your laptop it's plausible that you could use a cable. But as I said, this is all down to personal circumstances and taste!
I still use an ethernet cable to connect my desktop PC to my router for all the reasons I gave earlier, though I know this is a deeply unfashionable thing to do in the tech world. I suppose I'm a fan of using wires where possible. 😉