IMO, it is as much about starting out the project with mutual trust. I can understand why a shop might be wary of giving an estimate out over the phone. And from the customer's perspective, I would not be bringing my dream bike build to the shop that quotes the cheapest price, either. I would be looking to take it to a mechanic, or a shop that has proven its worth over time on smaller bike projects.

So back to what I said first about building mutual trust. Since you have a frame, why not bring it into the shop and tell them where you are in the process. talk to the mechanic who would be doing the work and see if you feel comfortable with him. Let him know what you already have, and what you need to get. Maybe he has some suggestions about component choices. Make him a partner in the process. It makes sense since they have to assemble and repair bikes, they might have some perspective on what works well together.