But any company that adopts SIP and promptly lays off its telecom team while shifting responsibility for voice to its IT team would be making a big mistake, according to Graham Francis, CIO of training and certification program. That's because people working in telecom teams have several skills that IT department workers might not possess, such supporting quality of service for real-time such as voice calls.

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"All the telecom guys are going to have to understand how voice and data will mix on the same network," says Francis, whose training sessions focus on areas such as SIP messaging, SIP , troubleshooting and interoperability. "People with TDM backgrounds need knowledge about data switches, firewalls and proxy servers. They need to understand that on a data network, voice just becomes another application."

While there is still definitely a place for telecom specialists in enterprises that use SIP trunks, they'll have to learn additional skills if they want to make a successful transition from TDM to SIP. In particular, they'll have to learn much more about traditional IT tools such as session border controllers and firewalls, since a SIP trunk is a broadband Internet link that utilizes SIP to connect a company's IP-based PBX to an Internet telephone service provider (ITSP). Instead of terminating the trunk directly at the IP-PBX, for security's sake companies tend to terminate the trunks at a SIP-capable session border control system that acts as a firewall.

Jim Maloff, the principal consultant for Maloff NetResults, says the biggest difference that telecom workers have to get used to when switching to SIP is thinking about phone calls in terms of bandwidth rather than available lines. This means that for large conference calls they'll need to figure out exactly how much bandwidth they'll need beforehand so they can provision it off and give it priority over other traffic on the network.