When will my lender run or obtain a copy of my credit report?
Your lender will run your credit report when you apply for a mortgage. (It cannot pull your credit report if you just call to ask about rates.) It will also pull your score again just before you close on a loan.
Be careful how you use credit between the time you apply for a mortgage and your loan closing. Opening a lot of new credit cards or maxing out existing cards, for example, can lower and damage your credit score significantly. This may affect the rate you can get on a mortgage.