Can this work this way?!
 

Hello everyone! I am going to try to explain here what I trying to do and I would like to hear suggestions on how this can be achieved.

THE SERVICES I USE:
Vono: Por que falar de outro jeito? - I have a braziliam DID number and I use this service to make/receive calls and it's configured in my ATA on SIP Account 1 and works fine!
FREE IP Calling with IPKall - I have a FREE US DID Number on this service been forwarded to FWD.
FWD | Home - I have this account setup on my ATA on SIP Account 2 and it works just fine also. On this line I receive calls from FWD and IPKALL and make calls using FWD.
http://www.netelip.com - I just signed up with this service and I got a DID in Spain and I want to use this VSP to make/receive calls also. I have a SIP URI in the following format <netelip_userid>@sip.netelip.com

IPKALL ISSUE:
IPKALL seems to accept forward only to Free World Dialup!!!
I tried <vono_userid>@vono.net.br and <netelip_userid>@sip.netelip.com on IPKALL configuration and won't work. When I call my IPKALL # I get busy signal. But if I forward it to my FWD account <fwd_userid>@fwd.pulver.com works fine!!!
ANY SUGGESTIONS HERE WHY DOES NOT WORK WITH OTHERS???

THE CHALLENGE:
With my ATA (Conectabox Zyxel P2602HWL-61C) letting me register with only 2 VSPs I though of Voxalot service!
So I created an account with Voxalot. Added all my VSP's listed above and created some Dial Plans. After this I configured SIP PORT 2 on my ATA to register with Voxalot. I went for some tests and everything seems to work smooth. I was able to make all the calls based on my dial plans configuration.
The only problem now is that voxalot will NOT ring my ATA!!! If anyone calls me on the VSPs I have added to my voxalot account my ATA/PHONE won't ring.

Do I have to go Voxalot Premium to be able to have voxalot register with my VSPs so people can call me and voxalot will RING my ata/phone?

For the DIDs that don't allow forwarding, yes.

However, for IPKall, you should be able to get it to ring by just telling IPKall to forward the call to your VoXaLot number, at the proxy voxalot.com

IPKall:

As DracoFelis said forward to
User: 123456 (replace for your VoXalot Number)
server: voxalot.com

FWD:

Can also be forwarded to sip:123456@voxalot.com

If the other 2 do not allow for such forwarding then you will need to upgrade to premium in order to receive calls on those two...(and enable SipRegistration for them)