Network/ports problem


I have an asterisk running with a voip sip gizmo account that works fine,
now I wanted to add a voipcheap account to sip.conf: no way to get it registered!

I switched off asterisk and used twinkle to acces directly the provider: error message that port 5060 is already in use, changed to port 5061, no help for voipcheap, but I can register with gizmo on port 5061!

what is happening here?

when I telnet gizmo on 5060, I get a connection
when I telnet gizmo on 5061, I get a connection refused, obvious, but why twinkle does it?
when I telnet voipcheap on 5060, it times out on trying…

any ideas?