I may be completely wrong on this, but I think this is someone who is reselling traffic (minutes) from a Betamax/Finarea company. Still the rates are quite competitive. There are slightly cheaper rates for Pakistan (less than 3p/min) if you just go directly with one of the Betamax providers whose rates can be found on:
http://backsla.sh/betamax.
Though the NYXFone calls are routed via VoIP (more specifically SIP), you also have a choice of local access numbers and also a useful callback that is triggered by a missed call. In comparison, Betamax do not really offer features like direct callback which is triggered this way. Callback for Betamax is normally triggered through their site(s) or via a Java client you can download onto your mobile or by SMS. (Exception is Betamax Returncall.co.uk, whose rates are pretty awful).
There is also another interesting thing I noticed which may be of some benefit to members here who have Indian connections. This company claims to have an Indian Toll free access number, which could potetially be a cheap way to make very cheap calls from India back to the UK. Not many VoIP companies provide one of these. They usually provide them in dozens of countries around the world, but India is rare!
Check out:
http://www.nyxfone.com/access_numbers.php