FXO port is used to connect to PBX or key system, or to provide off-premises connections to PSTN or PTT and supports battery reversal detection and caller ID. These Cisco VICs can be software configured to work in all countries. It is also used to connect to analog CAMA trunk to provide dedicated E-911 service.

The Cisco IP Communications voice/fax network modules provide enterprises, managed service providers, and service providers the ability to directly connect the public switched telephone network (PSTN) and traditional telephony equipment to existing Cisco 2600XM Series, Cisco 2691, 3640, and 3660, and Cisco 3700 Series voice gateway routers. This set of Cisco IP Communications voice/fax network modules delivers the most versatile combination of analog and digital voice and data capabilities in a single network module.The 4-port FXO voice/fax interface card is a universal card, which can be software configured to work in all countries. FXO port is used to connect to PBX or key system, or to provide off-premises connections to PSTN or PTT. Supports battery reversal detection and caller ID.