Pretty good for me. I use my iphone a lot for different purposes. It always last me the entire day.
Yes, the iphone will maintain a 3G connection and if you are in a Wifi network, it will maintain a connection to the Wifi network so that your call always comes through on the best possible connection you can. Does this seriously impact battery? No. When in standby my battery hardly diminishes. It can sit all day in standby and maybe drop like 20%. I haven't tested it but I certainly can for you. The point being, battery life has never been an issue for me.
Yes it can. iOS is really well designed. It can even maintain wifi in standby.
While you won't get 300 hours on standby, do you really need that?
Not for me. Instead of using the native phone app, I just use Talkatone. It does SMSs at the same time. Truth be told though, I prefer the native messaging client so I don't use talkatone's sms features. I use the SMS GV Extension. And if I want to facetime, I do it through the contacts app.
Of course I do. Talkatone reads the contacts from the phone so all your native contacts are always displayed in Talkatone and in the entire OS. So there is no issue here.
Yes those might be useless (but google voice offers those services and can be integrated in your usage of your iphone and talkatone, which also has some of that stuff). All things considered though, there is a price to pay to have everything so cheap. Without 3G in the mix, you basically have a free phone line and free messaging when in Wifi zones, like at home. There is no point to get a landline. And if you use a data plan, like we are talking about, the price is unbeatable. I only which the Phone GV Extension on cydia was as good as the SMS one. If someone could integrate talkatone into the native phone client it would be wonderful, but until that happens, I'd say this is quite a deal, just not perfectly seamless.