With so much being written about Voice over IP and Unified Communications, it's easy to forget that there are still lots of companies who, for various reasons, prefer to stick to traditional technologies. A fact I was reminded of when looking at research from Frost and Sullivan showing that TDM (Time Division Multiplexing) systems still accounted for 25% of total world PBX line shipments in 2010.

A lot of those sales will, of course, be to companies with old-style PBX systems yet to reach their sell-by date. Companies that will, ultimately, move to something newer but where use of SIP trunks and other add-ons isn't seen as cost-effective.

Others might be to companies yet to be convinced as to the merits of  VoIP or convergence, perhaps concerned about the quality and security implications. And yet more will, inevitably, be greenfield sales to buyers blissfully unaware that there are alternatives.

In terms of market split large enterprises are the most likely to have abandoned traditional TDM, seeing VoIP and, latterly,  Unified Communications as a way of gaining competitive edge for relatively modest outlay.

Lower down the scale, however, the required investment is proportionately much greater, and it's from small and medium sized businesses that much of future growth in IP based communications is likely to come.

It won't be huge, the Frost and Sullivan research showing a modest 4.4% annual increase in converged and native IP system shipments last year. But it's steady with the TDM share of the market expected to fall to less than 7% by 2017.

This article is written by Alan Stevens and sponsored by Avaya. The opinions reflected in this piece are solely those of Alan Stevens and may not reflect those of Avaya management