For point to point circuits I use PPP in a multilink PPP bundle.
For Frame, Nortel uses FRF.15 End-to-End Multilink Frame Relay, bundles at the PVC level. The Multi-link standards are primarily FRF.15 and FRF.16, but correct operation also involves FRF.5, FRF.8, and FRF.12. FRF.15 takes an 'end-to-end' approach to Multi-Link Frame Relay. The aggregate VC can be composed of multiple VCs taking divergent paths across different Frame Relay switches. This approach is more complex to implement and must make additional provisions for frames to be resequenced at the destination. Correct implementation includes use of the FRF.12 frame fragmentation standard, which may limit the ability of fragments to leave the Frame Relay environment and be carried over other services such as ATM. ( Note - Cisco does not currently have FRF.15-based devices, they do support the FRF.16 standard)