ISPhone are the ones to turn to for complete communication solutions. They specialise in IP telephony, fixed lines, mobile, and data services, along with a range of other communication services that will get your business operating more effectively.
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.