The Valcom V-2001A will work with the FXO port using MGCP. Configuration instructions are posted on the Valcom website at http://www.valcom.com/techsupport/ip_solutions/config-guides.htm . The instructions should work for all of the Valcom page controllers that use a loop-start trunk port, both single-zone and multi-zone controllers. If additional info is needed, the Valcom Technical Support department can be reached at support[at]valcom.com, or 1-800-valcom1.
Valcom also provides a full line of SIP-enabled speakers and gateways, which can interoperate with the legacy equipment. See the full line at www.valcom.com.
Full disclosure: this reply is being made by Valcom Technical Support.
Thank you.