Product Catalog: Telecommunications: ESI: Phone Systems Products ESI-600 (ESI) System for Converged Communications View Details IVX X Class (ESI) With up to 256 communications ports, IVX X-Class boasts the largest capacity among ESI's IVX (Integrated Voice Exchange) family of advanced business telecommunications systems. View Details IVX/IP E Class (ESI) Loaded with advanced capabilities yet amazingly easy to use, ESI's patented E-Class All-In-One Phone Systems give your business the power to present your most professional side to your customers. View Details IVX S Class (ESI) Loaded with advanced capabilities yet amazingly easy to use, ESI's patented IVX S-Class (IVX 56s) All-In-One Digital Phone System gives your small to medium-sized business the power to present your most professional side to your customers. View Details IVX C Class (ESI) The IVX C-Class All-In-One Digital Phone System is an easy choice over other phone systems in its class. View Details ESI Featured Phones (ESI) Having an ESI phone system lets you choose from among a variety of our attractive and highly convenient Feature Phones. View Details IVX E-Class Generation II (ESI) Built-in ACD; optional VoIP capabilities; up to 280 hours of voice message storage; up to 96 stations; up to 66 phone lines. View Details IVX S-Class Generation II (ESI) Up to 30 hours of voice message storage; up to 32 stations; up to 16 phone lines. View Details