Hi Vivek.
The FR Forum are going away from native VCoFR and the new upcoming things will be that your voice must be encapsulated in IP and then over FR. You need the FRF11 or even better FRF12 standards to carry voice over FR. The bigger vendors will, on VoIP, support both H.323 and SIP. SIP is the emerging standard from ETSI and 3GPP for UMTS or 3G mobile telephony. With UMTS Rel.5, it is pure IP, no more Circuit Switched. Put your money on VoIP, not over FR, but native IP. With the emerging CoS and QoS coming up for IP, you will not have a problem (MPLS, DiffServ etc.). The latest gig is AToM, All Traffic over MPLS, where you can carry IP, PPP, HDLC and ATM (AAL5 and AAL2).
Have a great day.
Peter.