I think it is best to do incremental estimates. "How long until you have the service deployed to staging with a single 'ping' operation?". When that step is c

I think it is best to do incremental estimates. "How long until you have the service deployed to staging with a single 'ping' operation?". When that step is complete: "Ok, now how long to get operation Foo working end-to-end?". This requires trust along the way that people aren't wasting time, but estimating a big project can really screw you. If the estimate comes back for 6 months, and it could have been done in 3, then the project will still take 6 months.