What is needed in Usings & References

If I want to call a method from another directive in code, what needs to be added to be able to call it?

I am in Quote.Update and want to call BpHolds.GetNewBpHoldAttachment. I do not want to use the BPM Workflow items because I need to do a while loop. I added Ice.Contracts.BpHolds as a reference, but it does not appear to work.