From a Voxalot/SIP point of view ozimarco is right. If it works that's great, however it might be worth double checking.

I've set up a couple of ZyXEL's...

Try putting in voxalot.com for SIP Server, Register Server and Sip Service and then click on the Advanced Setup button and make sure that the Outbound Proxy entry does not contain the name of your previous provider.

Infact, replace the Outbound Proxy Server address with eu.voxalot.com and set the port to 5060. I have found this is generally the easiest way.

On my Voice - Advanced Setting screen MarkLL, I have no Outbound Proxy Server field or something to put addresses in.

In the hope to clear everything that was previous put in my SIP1 configuration I have put back my account what was there before. Thats off sip.voipbuster.com.
When I put every data back I was immediate registered to voipbuster.com without pressing a button. Register/UnRegister is done in a few seconds.

Putting the data in for Voxalot and it wouldn’t work.
The trick for X-Lite to put @voxalot.com after User-Id under Authentication is not helping here.

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seems my memory was not so good. Sorry about that. The info Originally Posted by ozimarco was correct.

The Correct settings are: (for you)
SIP Server Address: eu.voxalot.com
REGISTER Server Address: eu.voxalot.com
SIP Service Domain: voxalot.com (although eu.voxalot.com also worked for me)

In Advanced settings do you have "URL Type" set to SIP?

Copy out of router:
System Name: P2032RLP1
ZyNOS F/W Version: V3.60(ADO.5) | 06/20/2007

I did have issues trying to use another ITSP so i emailed support and received new firmware. Try the settings above, if that does not work, contact Support and see if there is a firmware update.

Yes its working now.
 

Yes its working.

To make a long story short; it was a simple space behind the voxalot.com address in SIP Service Domain field.
The other two places with the eu.voxalot.com address have not that problem. There is still a spaces behind.
I think that I heaved copy the voxalot.com part with the space from those fields.

Thanks every one for helping out and take advantage off my mistake. ;)