According to a research by Dell'Oro Group, IP-PBX shipments will reach 28 million lines in 2006, surpassing time civision multiplexing (TDM)-based shipments.

Generally, in some TDM systems, successive pulses represent bits from successive channels, i.e., voice channels in a T1 system. In a few other systems, different channels take turns using the channels for a group of successive pulse-times (so-called 'time slot'). Primary distinguisher of coarse time-division multiplexing from packet switching is that the time-slots are pre-allocated to the channels, rather than interceded on a per-time slot basis.

According to analysts, while IP-PBX shipments will overtake those of TDM in 2006, the conversion of the installed base from traditional TDM systems will take time. Currently, more than 90 percent of the installed base is TDM and will still be the majority of the base throughout 2009.

With a conventional PBX, separate networks are necessary for voice and data communications. One of the main advantages of an IP-PBX is the fact that it employs converged data and voice networks. This means that Internet access, as well as VoIP communications and traditional telephone communications, are all possible using a single line to each user. This provides flexibility as an enterprise grows, and can also reduce long-term operation and maintenance costs. Like a traditional PBX, an IP-PBX is owned by the enterprise.

In the research firm's report, analysts believe that IP-telephone shipments have entered a period of sustained growth. The IP-telephone market will expand from simply a PBX handset business into an emerging IP-centrex and residential VoIP markets. Consumer wireless LAN (WLAN) phone introductions in 2005 will stimulate IP-telephone sales to residential VoIP subscribers.