Most business owners are unaware of the potential life of a telephone system for their small business.
Many phone systems we are replacing are 10-15 years old and potentially new phone systems could have an even longer life.
A modern phone system (or PBX) has less moving parts and is software driven; so the main driver for future replacement would be new available business features.
As new systems are software driven 99% of features will be made available simply by upgrading to a newer software level (such a mobex, or CTI screen popping). (Please read our post on Phone System Maintenance)
An obvious phone system benefit to us vendors in the industry is the prodctivity a PBX can add to a business, they far outweigh the small investment cost. Please see our post on phone system productivity.