Orbtalk have a range of SIP trunk products that work with the Linksys Cisco SPA2100
The SPA-2100 features two POTS (Plain Old Telephone Service) ports for connection to existing analog telephones, fax machines, PBX and key system communication platforms.
The SPA-2100 includes an Ethernet interface for connecting to a home or office PC (LAN) as well as an Ethernet connection to the broadband modem or router (WAN).
Stylish and compact in design, the SPA-2100 can be used in consumer and business IP telephony service offerings including full-featured IP Centrex.
The SPA-2100 delivers clear sounding voice and reliable fax calling through its implementation of internationally recognized standards for voice and data networking.