Digium 1A4A01F 4 Port Modular Analog PCI 3.3/5.0V Card The 1A4A01F from the A4 Series is a PCI card with EC for 3.3/5.0V with 0-FXS/0-FXO and 4 ports. This base PCI card for Digium's A4-series is scalable through expansion modules and can connect up to four interchangeable FXO or FXS modules. This base card also includes a carrier-grade echo cancellation unit for higher audio quality. Digium cards are compatible with all versions of Asterisk using the DAHDI driver framework. Asterisk and DAHDI are available for free from the Asterisk website. All cards include a five (5) year warranty and are eligible for Digium's Exceptional Satisfaction Program (ESP) risk-free Quality Guarantee.