This thread will be moved as soon as I found the place where to put this...

for your question:

I have a single phone at home which could do landlines and VoIP (Siemens Gigaset, DECT, chargers are seperate from base, AM), it does VoIP only atm as I don't have landlines... what the N900 is capable of you know already. A land-line-number from the US, one from Germany and two direct VoIP addresses are ringing at home so far...

so what you need is a phone at home that can do what you like to have! I suggest... buy one!

And there is GoogleVoice, still beta, still USA-only but it works...