mixed signal design flow

Mixed signal design is a system level development which have both analog and digital design.
For higher level system description and verification AMS , block level with spice (analog) and rtl(digital) based and full-chip level fast spice.there always have to have possibility of backannotation and postLO(extracted) info to be inserted flexibly and design flow should be able to support multiple views (hdl,schem,ext etc) of design flows.
With AMS environment it becomes quite convenient to manage and change the verification flow and not to mention system evaluation.
Mentor has ADvanceMS (AMS),eldo(spice type) and ADiT (fast spice) and all of them are tightly integrated and well suited for a typical Mixed signal flow.
Cadence has AMSdesigner(AMS),spectre(spice type) and Ultra sim (fast spice)
synopsys has DiscoveryAMS (AMS),HSPICE (spice level) and HSIM and nanosim(fast spice).
Magma has Finesim (spice) and Finesim-pro(fast spice)
generally it is possible to mix the tools as well.
Each of the design has its own peculiarities and so chip-level verification strategy is different for various designs.You have to foresee the issues while deciding upon the way to take and setup your verification flow as wrong choices cost time and tedious workarounds.