You can use AIM-COMPR2 for voice compression as described in the following section of the document with certain restriction and limitations described in this dcoument.
Hardware Compression and Software Compression Interoperability The Frame Relay Fragmentation with Hardware Compression feature provides hardware and software compression interoperability when hardware compression is configured on one side of the link and software compression is configured on the other side.
Benefits
The Frame Relay Fragmentation with Hardware Compression feature makes hardware compression available to networks that transmit voice and to other networks that use fragmentation. Hardware compression, though functionally equivalent to software compression, provides the benefit of offloading computationally intensive compression algorithms from the CPUs of routers, freeing up bandwidth for other functionality and features.
Restrictions
Voice over Frame Relay and Voice over IP packets will not be payload-compressed when Frame Relay fragmentation is configured. On VCs using IETF encapsulation, FRF.9 hardware and software compression will work with Frame Relay fragmentation but will not work with header compression.
http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121newft/121t/121t5/dtfrfwhc.htm
