Linksys by Cisco, a division of Cisco Systems, is a manufacturer of a line of popular VoIP (Voice over IP) adapters. These Voice over IP analog adapters have continued to grow in favor with service providers and end users thanks to their ease of use and reliability.

The Linksys line of adapters is called the SPA series. The SPA series was originally the product of Sipura technologies, an early VoIP start-up that was acquired by Linksys. The core technology behind the Sipura adapters is still the same technology used inside of a Linksys adapter.

Although there have been numerous models, the current VoIP adapter offerings within the series is comprised of three different devices. These include:

• PAP2T - The Linksys PAP2T is the most commonly used device of the three offerings. It originally gained acclaim as the defacto device for use with Vonage. The PAP2T comes with two (2) FXS ports for the connecting of telephones and a single Ethernet port for Internet connectivity. The device can be used with any SIP based service provider and retails for around $55 USD.
• SPA2102 - The Linksys SPA2102 is similar to the form and function of the PAP2T, but features an additional Ethernet port (for LAN/WAN connections). While not as popular as the PAP 2T (primarily due to it being a little more expensive), the SPA2102 is a popular option for many service providers and end users in need of a second Ethernet port. It is also SIP compatible and can be found online for around $70 USD.
• SPA3102 - Last but not least, the SPA3102 is the most advanced VoIP adapter from Linksys. The SPA3102 features a single FXS port and a single FXO port, allowing for the connection of a POTS line. This allows those using the device to have a fail over should their network or Voice over IP service go down. With this added functionality comes an increase in price (can be purchased for about $75), but the extra couple of dollars is worth every penny - especially if you're worried about service outages.

Obviously this is just a general overview. More specific information can be found through the Linksys website, your favorite voice over ip service provider or through equipment suppliers like VoIP Supply.