VoFR is still an evolving technology overall. The specifications have a number of variables left open to vendor interpretation. As long as each individual vendor is FRF.11- and FRF.12-compliant, interoperability should be a viable solution. It doesn't always work that way, however. As in any solution, the more univendor you can keep the installation, the fewer problems you are likely to have.
In planning to implement this technology, examine the specifications. They are remarkably easy to read and well organized, and are less of a cure for insomnia than most other specifications out there. And, you'll learn something new each time you read them.
The best thing that can be done in planning a VoFR implementation is due diligence. Make sure all the research is complete and that all questions have been adequately answered. Don't simply take the word of sales representatives.
The overall intention of this document is to outline some of the fundamentals of VoFR technology. For more background on Cisco's implementation of VoFR, check out http://www.cisco.com and perform a search on "Voice over Frame Relay" or "VoFR." For additional information regarding FRF.11 and FRF.12, visit http://www.frforum.com.