Adtran was synonymous with the CSU/DSU market and in fact they had a virtual monopoly on the space for years. As markets change however companies need to evolve and as the CSU/DSU market slowly eroded, Adtran looked to other areas in which to thrive.
One of these areas it turns out is VoIP. Adtran has a number of products that complement IP PBXes nicely -- their NetVanta series 1000 managed layer 2 Ethernet switches. These devices come in a number of flavors and sizes and can be purchased directly by an enterprise or by service providers for resale. One is sure to suit the palette of your IT department. The Netvanta 1224STRPoE is a great product because it is a switch, a router, and has power over Ethernet known as 802.3af. It’s a non-blocking switch, has 24 ports of fast Ethernet interfaces. It's 1U in size, rackmountable and of course 19". The price is a surprise. Surprisingly low that is. It lists for $2,295. Take away POE and the price drops $1k. The warranty is five years and the software upgrades are free for life. The company is almost giving these products away but when you compete with Cisco and more recently Dell you need to differentiate yourself and Adtran seems to be doing a good job of this.