Ok, will answer the last question first. At home I have Asterisk, number of ATAs, Siemens Gigaset S450 IP and Nokia E60. Let's forget about this for now
The idea is to make myself reacheable when I'm travelling. As soon as I cannot (and do not want) to rely on my home Asterisk (mainly because of possible ISP problems) I want VoXaLot to do some job for me.
So, when I'm in a hotel room or in the office I can have my softphone and Nokia registered at VoXaLot so I'll be able to answer my incoming calls.
When I'm away from my PC but within WiFi coverage I will still have E60 working (until something broken at your side).
And now imagine that all you Nokia workarounds will not work like I've seen this today - I've been able to register and make some test calls but after few hours registration is ok, but no sound and no incoming calls even when I see that NAT pinhole is open on my router. That's why I was looking for possibility to forward the call to the SIP URI which will be the same Nokia phone but registered with another VSP.
But as soon as I'm out - I need my calls transferred to my cell phone. This time it will be US number with NYC area code. In this particular case I can let GC do some job for me, but next time I will use my European cell phone with UK number, so GC will not ring that phone. And GC will not help me completely - it will ring my SIP and my cell if somebody dialed my GC number, but what if somebody will make a SIP call to my voxalot id ? SIP will ring, but not cell.