The service allows hiding the number from which you are calling. Thus,
you ensure yourself a guarantee that your number does not come to a
telemarketing agency and you won’t be troubled by endless calls with offers.
Obviously SIP is considerably better than H.323 and complies with the understanding of IP-telephony as a global mass IP-service, and it should be implicitly considered right this way. And as SIP is able to serve not only telephony but also any communications at all in the real time over the IP-protocol; obviously it should become a base for other IP-services not yet existing but will appear in the future, as well.