Telecom transformers are found in devices needing strong bandwidths and rapid switching places. Their function revolves about isolating the signals amidst primary and secondary grounds. Such transformers are DSL transformers (cater to the Digital Subscriber Loop), ISDN transformers (as seen in the Integrated Services Digital Network), LAN transformers (Local Area Network) and ATM transformers (Asynchronous Transfer Mode).

Serving as isolation transformers, Telecom transformers changes the voltage making it more compatible for lower voltage applications. How well a telecom transformer performs is determined by insertion loss (the ratio between the power generated by the power took in by the device), isolation (or high potential) degree, frequency width, resistance to Direct Current, functioning temperature as well as size.

These transformers come in various packaging forms and methods.  They can be packed in Integrated Circuit (IC) package forms such as flat pack, single-in-line, dual-in-line and small outline integrated circuits. Alternatively, surface mounted technology and through hole technology can be applied to board-level transformers.

Common packing methods are trays, tubes, and tape and reel kits.