Sulkin, Allan (January 1, 2003). "PBX market-the shift to IP is on". Business Communications Review. 33 (1): 21. Archived from the original on October 22, 2012. Retrieved 16 December 2008.
Sulkin, Allan (January 1, 2003). "PBX market-the shift to IP is on". Business Communications Review. 33 (1): 21. Archived from the original on October 22, 2012. Retrieved 16 December 2008.